WASHINGTON – The FBI has been quietly investigating the Clinton Foundation for months, reviving a probe that was dialed back during the 2016 election amid tensions between Justice Department prosecutors and FBI agents about the politically charged case, according to people familiar with the matter.

The investigation is being run out of the FBI's field office in Little Rock, Ark., where the foundation has offices in the William J. Clinton Presidential Center, the sources said. Agents are trying to determine if donations made to the foundation were linked to official acts when Hillary Clinton was secretary of state from 2009 to 2013, they said.

It was not immediately clear what specific donations or interactions agents were scrutinizing, and there was some skepticism inside both the Justice Department and the FBI that the case would ultimately lead to any charges.

The very existence of such a probe will likely lead to accusations­ from Democrats that the Trump administration is pursuing old, dead cases to punish political enemies.

President Donald Trump has repeatedly urged the Justice Department to prosecute Clinton and her aides. But while the Clinton Foundation investigation was effectively stopped in 2016, the move at the time was described by people familiar with the matter as temporary because Justice Department officials were concerned that if details of the probe became public, it would appear that investigators were trying to hurt Clinton's chances in the election.

Foundation spokesman Craig Minassian said in a statement: "The Clinton Foundation has been subjected to politically motivated allegations, and time after time these allegations have been proven false. None of this has made us waver in our mission to help people. … There are real issues in our society needing attention that the Clinton Foundation works hard to solve every day. So we're going to stay focused on what really matters."

Republicans have long raised concerns about what they viewed as corruption and conflicts of interest at the Clinton Foundation, in particular Hillary Clinton's dealings with its donors while she was secretary of state.

The Clinton Foundation probe dates back to 2015, when FBI agents in Los Angeles, New York, Little Rock and Washington began looking at a variety of different figures who had made donations to the charity, according to people familiar with the matter. In 2016, Justice Department prosecutors rejected a request from FBI agents to expand and intensify the investigation.

Republican lawmakers had called on Attorney General Jeff Sessions in July and again in September to explore various Clinton Foundation dealings, as well as other matters, by appointing a special counsel. In November, the Justice Department wrote that Sessions would direct prosecutors to look into the cases about which they raised concerns and hinted that some were already under scrutiny.

Assistant Attorney General Stephen Boyd wrote that the department would assess whether "matters currently under investigation require further resources."

By that time, according to the people familiar with the matter, agents were already investigating the foundation.

The Clinton Foundation inquiry is separate from the FBI's high-profile investigation into Hillary Clinton's use of a private e-mail server while she was secretary of state, though Republicans have said that probe, too, needs to be reopened. The e-mail investigation focused on whether Clinton or her aides mishandled classified information by using the private server. Then-FBI Director James Comey recommended in July 2016 the case be closed without charges.

Justice Department officials have said senior prosecutors are also reviewing investigative records on the Clinton e-mail case to see if any of the concerns raised by Republican lawmakers merit appointment of a special counsel.

Word of the ongoing foundation probe came after Rep. Mark Meadows, R-N.C., and Rep. Jim Jordan, R-Ohio, said Thursday that it might be time for a new attorney general.

Trump has publicly toyed with removing Sessions, and he has repeatedly criticized the Justice Department and said his attorney general should look into Clinton and her allies, taking aim most recently at top Clinton aide Huma Abedin. On the campaign trail, Trump specifically called for a special counsel to investigate the foundation.

"Let's call this what it is: a sham," Hillary Clinton spokesman Nick Merrill said. "This is a philanthropy that does life-changing work, which Republicans have tried to turn into a political football. … The goal is to distract from the indictments, guilty pleas, and accusations of treason from Trump's own people at the expense of our justice system's integrity. It's disgraceful, and should be concerning to all Americans."