This story was co-produced with NPR News.

Freddie Mac agreed last month to stop making new bets against American homeowners after its regulator, the Federal Housing Finance Agency, raised concerns, according to a statement the agency issued late Monday. Freddie, the taxpayer-owned mortgage giant, still retains $5 billion worth of such bets.

The agency, responding to an investigation by ProPublica and NPR, said it had "identified concerns regarding the controls, including risk management, surrounding the inverse floaters," as the investments at issue are known. The agency did not specify what it had found, but said Freddie agreed in December that "these transactions would not resume pending completion of [FHFA's] examination work." The statement also said that Freddie had ceased making the deals earlier in 2011 but did not explain why.

Separately, the White House said the Department of the Treasury is "looking into" Freddie's investments, and at least three senators called on Freddie not to bet against struggling homeowners.

The mortgage-insurance company bought billions worth of complex mortgage-backed securities that profit if borrowers stay trapped in high interest rate home loans. The $5 billion figure released Monday afternoon is more than had been reported in the ProPublica-NPR investigation.

In late 2010 and early 2011, Freddie began dramatically increasing these multibillion-dollar deals. At the same time, Freddie also made it harder for homeowners to get out of their high-interest mortgages and into more affordable loans that could save them thousands of dollars a year. No evidence has emerged that these decisions were coordinated at the company, and Freddie has denied that they were.

But the deals highlight a conflict of interest: While Freddie's charter calls for the company to make home loans more accessible, the company also has giant investment portfolios that could lose large amounts of money, at least in the short run, if too many borrowers refinance into more affordable loans.

At a press briefing today, White House spokesman Jay Carney was asked whether Freddie Mac's investment strategy contradicted President Barack Obama's stated commitment to make homeowner refinancing more affordable. In his response, Carney stressed that the president does not directly control FHFA.

"This is an independent institution with independent governance, so we don't make those kinds of decisions," Carney said.

Meanwhile, Sen. Bob Casey, D-Pa., sent a letter to the White House today demanding an explanation of the Freddie Mac investments. Referring to the head of the company, the senator wrote, "I question the leadership that would position the government-backed organization to bet against homeowners."

Sen. Casey wants the administration to "exercise influence over the FHFA, and make sure that Freddie is not making these kinds of bets," his spokesman said.

Sen. Johnny Isakson, R-Ga., said in an interview that if Freddie "bet on keeping everybody in the loans they're in, and not allowing them to refinance, that would be wrong. Particularly for those people that are qualified to refinance." And Barbara Boxer, D-Calif., fired off a letter to the acting director of the FHFA expressing "outrage" over Freddie's deals.

In its statement today, the FHFA confirmed that Freddie, in making these investments, retained significant risks. When Freddie was taken over by taxpayers in 2008, Freddie Mac entered into an agreement with the U.S. Treasury to reduce the company's investment holdings. The inverse floater deals leave "Freddie Mac with a portion of the risk exposure it would have had if it simply held the entire set of mortgages on its balance sheet," the FHFA said.

In fact, mortgage experts said that inverse floaters burden Freddie with new risks. With these deals, Freddie has taken mortgage-backed securities that are easy to sell and traded them for ones that are harder and possibly more expensive to offload.

ProPublica and NPR found $3.4 billion of Freddie's inverse floater deals, and their value is based mostly on interest payments on $19.5 billion of mortgage-backed securities. The new statement suggests that Freddie retained exposure to greater than $19.5 billion, but it is unclear how much more.