Bulgaria's announcement today that investigators suspect Hezbollah in last summer's terrorist bombing against Israeli tourists on the Bulgarian coast ratchets up a conflict between the West and Iran that is being waged in political, military and covert arenas.

Half a year after the bombing killed six people and wounded 30, the results of the investigation suggest the attack was the Lebanese militant group's first terror strike on European soil since the 1990s.

As ProPublica reported last summer Iran and Hezbollah have waged a covert global struggle with Israel and the United States for the past several years as a result of conflict over Iran’s nuclear ambitions. Israel and the United States reacted to Tuesday's news from Bulgaria by repeating calls for the European Union to designate Hezbollah as a terrorist group — a move that most EU nations have resisted.

The investigation into the July 18 attack in Burgas, a popular coastal destination for Israelis, has been slow and difficult despite the support of Israeli, U.S. and European counterterror agencies, according to officials familiar with the case.

Bulgarian interior minister Tsvetan Tsvetanov made a public statement Tuesday revealing that, while some questions have been answered, others persist.

Investigators have determined that the bomber, who died in the attack, and two accomplices traveled from Lebanon via other European countries to Bulgaria carrying fraudulent Michigan driver's licenses fabricated in Lebanon, according to Tsvetanov.

Two of the suspects traveled via Germany and Belgium, according to a U.S. counterterror official who requested anonymity because he was not authorized to speak about the case. Bulgarian investigators retraced movements of the trio from June 28, when they entered the country and used the fake licenses at hotels and to rent cars, until July 18, when a backpack carried by a lanky, long-haired youth in casual attire blew up the bus carrying Israeli tourists at the Burgas airport, according to Tsvetanov.

Investigators have identified the bomber's accomplices, whose licenses bore the aliases Ralph William Rico and Brain Jameson, as holders of Australian and Canadian passports. The two, now fugitives, have lived and worked in Lebanon since 2006 and 2010 and are believed to be Hezbollah operatives, the interior minister said.

"We traced their overall activity in Australia and Canada," Tsvetanov said. "We have data on financial links and involvement in Hezbollah. What can be made as a reasonable assumption — I repeat, a reasonable assumption — is that the two persons whose real identity was established belonged to the military formation of Hezbollah."

The Australian is a man of Lebanese descent whom Western law enforcement has been hunting in recent weeks, according to a European counterterror official familiar with the investigation. The Bulgarian interior minister said his country will request help from Lebanon, Australia, Canada and other countries as the investigation continues.

The profile of the suspects fits a pattern of Hezbollah using operatives with Western passports, counterterror officials say. Cypriot authorities are prosecuting a Swede of Lebanese descent for conducting reconnaissance on Israeli tourists last year. In 2009, Turkish police arrested a suspected Canadian Hezbollah operative in a failed car bombing against an Israeli diplomatic target.

Although the Bulgarian interior minister said investigators had recovered DNA traces of all three suspects, it was not clear whether the bomber, whose alias was Philip Martin, has been identified.

Tsvetanov also did not address the mystery of whether the attack was a suicide bombing. The explosive device carried a mechanism enabling it to be detonated from afar, according to the European counterterror official. Some Western investigators believe the bomber did not intend to die, but rather that an accomplice set off the bomb prematurely, in response to unforeseen circumstances or because the bomber was a dupe.

"The discovery of his license makes it more likely that he was not a suicide bomber," the European counterterror official said. "If it had all been planned to happen exactly as it did with his knowledge, I think they would have taken the license away to make it harder to trace him. We think it is an attacker who died rather than a voluntary kamikaze."

Although Hezbollah has conducted suicide car bombings against hard targets, it generally does not carry out lone-bomber suicide attacks on foot, said Magnus Ranstorp, a foremost Hezbollah expert at the Swedish National Defense College.

Hezbollah has used unwitting bombers before, he said, adding that there are "odd things" about the attack that have yet to be explained, such as the clumsily forged licenses.

But he and other experts said the timing, target and profile of the suspects suggests the attack was part of an escalating offensive by Iranian spies and Hezbollah militants that has resulted in attacks and plots from Africa to India to Thailand.

The shadow war has intensified because of Israeli assassinations of Iranian nuclear scientists and of Imad Mughniyeh, a Hezbollah warlord with close ties to the Iranian security forces, in 2008. The Burgas attack happened on the 18th anniversary of a massive car-bomb in Argentina carried out by Iranian and Hezbollah operatives in 1994.

Although Europe supports U.S. and Israeli efforts to thwart Tehran's nuclear ambitions, the European Union's policy toward Hezbollah diverges considerably. Most European nations resist pressure to designate Hezbollah, even its military wing, as a terrorist organization. In a clear sign of that reluctance, EU foreign minister Catherine Ashton issued a response to the Bulgarian announcement Tuesday that did not use the word Hezbollah.

Even European Union nations that view Hezbollah as a threat worry that designation could spur retaliation and destabilize Lebanon, where the militant group wields considerable power in government and on the street, Ranstorp said. European leaders also worry about the complex conflict with Iran involving Syria's civil war and the Iranian nuclear program.

"It's not a stand-alone issue," he said. "It's wrapped up in what's happening with Syria, Israel and above all, Iran."