July 18: This post has been corrected.

Last year, Iranian President Mahmoud Ahmadinejad visited his ally President Hugo Chavez in Venezuela, where the firebrand leaders unleashed defiant rhetoric at the United States.

There was a quieter aspect to Ahmadinejad's visit in January 2012, according to Western intelligence officials. A senior officer in the Iranian Revolutionary Guards Corps (IRGC) traveled secretly with the presidential delegation and met with Venezuelan military and security chiefs. His mission: to set up a joint intelligence program between Iranian and Venezuelan spy agencies, according to the Western officials.

At the secret meeting, Venezuelan spymasters agreed to provide systematic help to Iran with intelligence infrastructure such as arms, identification documents, bank accounts and pipelines for moving operatives and equipment between Iran and Latin America, according to Western intelligence officials. Although suffering from cancer, Chavez took interest in the secret talks as part of his energetic embrace of Iran, an intelligence official told ProPublica.

The senior IRGC officer's meeting in Caracas has not been previously reported.

"The aim is to enable the IRGC to be able to distance itself from the criminal activities it is conducting in the region, removing the Iranian fingerprint," said the intelligence official, who requested anonymity because he is not authorized to speak publicly. "Since Chavez's early days in power, Iran and Venezuela have grown consistently closer, with Venezuela serving as a gateway to South America for the Iranians."

A year and a half later, Chavez has died and Ahmadinejad is no longer president. But the alliance they built is part of an Iranian expansion in the Americas that worries U.S., Latin American, Israeli and European security officials.

Experts cite public evidence: intensified Iranian diplomatic, military and commercial activity in the region; the sentencing this year of an Iranian-American terrorist in a plot to assassinate the Saudi ambassador in Washington; U.S. investigations alleging that Hezbollah, Iran's staunch ally, finances itself through cocaine trafficking; and a recent Argentine prosecutor's report describing Iran's South American spy web and its links to a 2007 plot to bomb New York's JFK airport.

There is considerable debate inside and outside the U.S. government about the extent and nature of Iran's activities, however. That debate dominated a U.S. congressional hearing this week about a new State Department report that assesses the Iranian threat in Latin America, a region made vulnerable by lawlessness and an increasingly anti-U.S. bloc of nations.

The report resulted from a bipartisan bill, the Countering Iran in the Western Hemisphere Act, signed into law by President Obama in January. That measure called for a comprehensive U.S. response to Iranian incursions and a study based on threat assessments by intelligence and law enforcement agencies. Most of the study is classified. A two-page unclassified section says that "Iran has increased its outreach to the region working to strengthen its political, economic, cultural and military ties."

Nonetheless, the State Department assessment concludes that "Iranian influence in Latin America and the Caribbean is waning" as a result of Western sanctions, U.S. cooperation with allies and "Iran's poor management of its foreign relations."

In a recent interview about the issue, a senior U.S. government official gave a measured assessment comparable to the new report.

"The countries of the region need to watch carefully for Iran as a threat within a spectrum of issues of concern in the region," said the official, who was not authorized to speak publicly. "I don't see it as a major threat now. This is worth watching. It is something there is legitimate attention to given Iran's history."

The law's sponsor, Rep. Jeff Duncan, R-S.C., criticized the State Department's findings Tuesday at a hearing of a House homeland security subcommittee that he chairs. Duncan does not think Iranian influence has declined so soon after a series of events and trends — including recent public warnings by intelligence and Pentagon chiefs — that brought about the passage of the Countering Iran Act.

"This administration refuses to see Iran's presence — so near U.S. borders —as a threat to U.S. security," Duncan said. "We know that there is not consensus on this issue, but I seriously question the administration's judgment to downplay the seriousness of Iran's presence here at home."

State Department officials contacted by ProPublica declined to respond because the report is classified. They said they will discuss the issue with legislators in private.

As a sign of growing Iranian influence in South America, Duncan cited the absence of a key witness at the hearing: Alberto Nisman, an Argentine special prosecutor.

In May, Nisman released a 502-page report as part of a long investigation of a car-bombing that killed 85 people at the AMIA Jewish community center in Buenos Aires in 1994 — the deadliest terror attack in the Americas before 2001. The report describes the evolution of Iranian spy networks in the region and shows their role in attacks in Argentina and the foiled New York airport plot.

Although Nisman had initially accepted the congressional invitation to discuss his investigation, last week his government abruptly barred him from traveling to Washington. The Argentine attorney general said that the topic of the hearing "had no relation to the official mission of the [Attorney General's] office," Nisman wrote in a July 1 letter to Rep. Michael McCaul, R-Texas, chairman of the House Committee on Homeland Security.

"The government of Argentina has silenced this prosecutor," McCaul declared at the hearing Tuesday. "I consider this to be a slap in the face of this committee and the U.S. Congress."

Expressing disappointment in a letter to Argentine President Cristina Fernández de Kirchner, McCaul and Duncan said the attorney general's decision "[calls] into question the authenticity of your intentions" to "pursue justice and truth on Iranian involvement in the AMIA bombing."

The context for the unusual move to block the testimony is Argentina's pro-Iranian shift. Argentina has had tense relations with Iran since the AMIA attack. A previous bombing in 1992 — also blamed on Iran — destroyed the Israeli embassy in Buenos Aires and killed 29 people.

In 2003, Nisman was appointed special prosecutor with a mandate to revive a probe that had bogged down in dysfunction and corruption. He indicted seven Iranian officials and a Hezbollah chief as the masterminds three years later, and Interpol issued arrest warrants for them. Iranian officials denied any role and described Nisman, who is Jewish, as "a Zionist."

But six months ago, the Fernández de Kirchner government agreed with Iran to form an independent "truth commission" about the AMIA case. Argentina's about-face was blasted by Jewish groups, the political opposition, the Israeli government and U.S. officials. Critics call it a political maneuver that makes justice even less likely at this late date. Argentina's growing ties to Iran coincide with an increasingly confrontational attitude toward the United States, Spain and other Western nations.

"The Argentine president has already made her decision to curtail DEA activities, publicly and repeatedly attack the United States as an imperialistic and warmongering nation, and reopen relations with Iran that make a mockery of the rule of law," Douglas Farah, president of the IBI Consultants national security consulting firm, testified at the hearing.

Duncan said in an interview that he believes Argentina's policy change results partly from economics. Iran-Argentine trade has increased by more than 500 percent to $1.2 billion annually in the past eight years, according to the testimony of Ilan Berman, vice president of the American Foreign Policy Council, a think-tank in Washington.

The attacks in Buenos Aires in the 1990s revealed the existence of Iranian terror networks in the Americas. The Argentine investigation connected the plots to hubs of criminal activity and Hezbollah operational and financing cells in lawless zones, such as the triple border of Argentina, Brazil and Paraguay and the border between Colombia and Venezuela.

Indicted AMIA plotter Mohsen Rabbani, an alleged spymaster using the cover of Iranian cultural attaché in Buenos Aires, oversaw the establishment of intelligence networks in embassies, front companies and religious and cultural centers in Argentina, Brazil, Colombia, Chile, Guyana, Paraguay and Uruguay, according to the Argentine prosecutor's report. The Iranian spies teamed with Hezbollah to carry out both bombings, according to Argentine, Israeli and U.S. investigators.

Today, the fugitive Rabbani is based in Iran and continues to play a key role in Latin American espionage, directing ideological and operational training for recruits who travel from the region, according to U.S. law enforcement officials and witnesses at the hearing.

The election of Ahmadinejad in 2005 spurred an Iranian outreach campaign in Latin America intended to find new allies and markets and counter Western pressure over Iran's nuclear ambitions, according to Berman. Iran increased the number of its embassies in the region from five to 11, launched a Spanish-language television channel and doubled its regional trade to $3.67 billion today, though many of its economic commitments have not materialized.

The Iranian expansion dovetailed with the rise of the Bolivarian Alliance for the Americas (known by the Spanish acronym as ALBA), a bloc of leftist, populist, anti-U.S. governments including Venezuela, Cuba, Bolivia, Ecuador and Nicaragua.

 In 2008, the U.S. Treasury Department designated a Venezuelan diplomat and a Venezuelan businessman as terrorists for allegedly raising funds for Hezbollah, discussing terrorist operations with Hezbollah operatives, and aiding travel of militants from Venezuela to training sessions in Iran. In 2011, Iranian Defense Minister Ahmad Vahidi, who is wanted by Interpol for the AMIA bombing, attended the inauguration of ALBA's regional defense school in Bolivia, according to testimony at the hearing.

The FBI and DEA teamed up that same year to foil a plot in which commanders of the Quds Force, the external operations wing of the IRGC, were charged with directing an Iranian-American operative to use Mexican cartel gunmen to kill the Saudi ambassador in Washington. Director of National Intelligence James Clapper told the U.S. Senate in January 2012 that the assassination plot “shows that some Iranian officials — probably including Supreme Leader Ali Khamenei — have changed their calculus and are now more willing to conduct an attack in the United States."

At a hearing of the House Foreign Affairs Committee days later, U.S. Rep. Ileana Ros-Lehtinen, then the committee chairman, warned that Iran's Latin American alliances could pose "an immediate threat by giving Iran — directly through the IRGC, the Quds Force [an external unit of the IRGC] or its proxies like Hezbollah — a platform in the region to carry out attacks against the United States, our interests, and allies."

The aborted 2007 plot to attack JFK was an attempt to use that platform, according to the Argentine special prosecutor. A Guyanese-American Muslim who had once worked as a cargo handler conceived an idea to blow up jet fuel tanks at the airport. He formed a homegrown cell that first sought aid from al Qaida, then coalesced around Abdul Kadir, a Guyanese politician and Shiite Muslim leader.

The trial in New York federal court revealed that Kadir was a longtime intelligence operative for Iran, reporting to the Iranian ambassador in Caracas and communicating also with Rabbani, the accused AMIA plotter.

"Kadir agreed to participate in the conspiracy, committing himself to reach out to his contacts in Venezuela and the Islamic Republic of Iran," Nisman's report says. "The entry of Kadir into the conspiracy brought the involvement and the support of the intelligence station established in Guyana by the Islamic regime."

Police arrested Kadir as he prepared to fly to Iran to discuss the New York plot with Iranian officials. He was convicted and sentenced to life in prison.

The Argentine investigation unearthed other signs of Iranian terrorist activity. It cites the testimony of the former director of Colombia's intelligence agency, Fernando Tabares. He described a mission by an Iranian operative to Colombia via Venezuela in 2008 or 2009. Working with Iranian officials based at the embassy in Bogota, the operative "was looking at targets in order to carry out possible attacks here in Colombia," Tabares testified.

Witnesses at the House subcommittee hearing Tuesday described Venezuela as a gateway through which Iranian operatives travel to and from the region unmolested and obtain authentic Venezuelan documents to enhance their covers.

Witness Joseph Humire, a security expert, cited a report last year in which the Canadian Border Services Agency described Iran as the top source of illegal migrants to Canada, most of them coming through Latin America. Between 2009 and 2011, the majority of those Iranian migrants passed through Caracas, where airport and airline personnel were implicated in providing them with fraudulent documents, according to the Canadian border agency.

The allegations are consistent with interviews in recent years in which U.S., Latin American and Israeli security officials have told ProPublica about suspected Middle Eastern operatives and Latin American drug lords obtaining Venezuelan documents through corruption or ideological complicity.

"There seems to be an effort by the Venezuelan government to make sure that Iranians have full sets of credentials," a U.S. law enforcement official said.

Last year's secret talks between Iranian and Venezuelan spies intensified such cooperation, according to Western intelligence officials who described the meetings to ProPublica. The senior Iranian officer who traveled with the presidential entourage asked Venezuelan counterparts to ensure access to key officials in airport police, customs and other agencies and "permits for transferring cargo through airports and swiftly arranging various bureaucratic matters," the intelligence official said.

Venezuelan leaders have denied that their alliance with Iran has hostile intent. They have rejected concerns about flights that operated for years between Caracas and Tehran. The State Department and other U.S. agencies criticized Venezuela for failing to make public passenger and cargo manifests and other information about the secretive flights to Iran, raising the fear of a pipeline for clandestine movement of people and goods.

The flights have been discontinued, U.S. officials say.

State Department officials say the Iran report reflected a consensus among U.S. government agencies. In contrast, homeland security Chairman McCaul said the intelligence community is more concerned about the Iranian threat than the State Department.

The DEA and Treasury Department have been especially active on the issue. Recent indictments and enforcement actions have revealed a complex global network of cocaine trafficking and money laundering networks that allegedly poured millions of dollars into the coffers of Hezbollah in Lebanon. Those mafias, led by accused gangsters of Lebanese origin operating in Colombia, Venezuela and Panama, allegedly have links to the Iranian government as well, according to U.S. court documents.

The State Department says a concerted effort by diplomats, intelligence officers and law enforcement investigators has stymied Iran's advances. The end of the personal bond between Chavez and Ahmadinejad was another blow, officials say.

"The death of … Chavez and the election of a new president in Iran has changed the landscape of Iran's relationship in Venezuela and further weakened Iranian ties in the West," said Rep. Bennie Thompson, D-Miss., the ranking member of the Homeland Security Committee.

The foreign policy of new Venezuelan President Nicolas Maduro is a work in progress. But as Duncan and others pointed out this week, Maduro was a point man for the alliance with Iran when he led served as foreign minister from 2006 to 2012.

Correction: Due to an error in testimony by a congressional witness, this story initially misattributed a statement made by Rep. Ileana Ros-Lehtinen, R-Fla., to James Clapper, the Director of National Intelligence. The story has been revised to correct the attribution and incorporate Clapper’s actual statement to a Senate committee.