The Justice Department is investigating whether the Clinton Foundation engaged in any "pay-to-play" politics or other illegal activities while Hillary Clinton served as Secretary of State, according to reports.

FBI agents from Little Rock, Arkansas, where the Foundation was launched, are reportedly leading the inquiry, and have interviewed at least one witness within the last month, The Hill reports, citing unidentified law enforcement officials and a witness.

The officials, who would only speak on the condition of anonymity, told the newspaper the probe is investigating whether the Clintons promised or performed any policy favors in return for donations or gifts. They said it may look at whether any tax-exempt assets were used for personal or political gain and whether the Foundation operated in compliance with applicable tax laws.

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One witness who told The Hill they were recently interviewed by the FBI said the line of questioning was focused around donations to Clinton entities in the period when Clinton was in charge of President Barack Obama's State Department.

The witness said investigators also specifically wanted to know whether donors to the Clinton's charitable efforts received any "favorable treatment" from the Obama administration on a policy decision they said had been previously highlighted in media reports.

The Department of Justice and FBI headquarters in Washington did not immediately respond to a request for comment.

It comes after reports emerged on Thursday that Justice Department officials would once again be probing Clinton's use of a private email server during her time as secretary of state.

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An ally of Attorney General Jeff Sessions described the probe as a way of gathering new information about the handling of classified documents by Clinton and her aides, in an interview with the Daily Beast.

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Throughout his presidential campaign and almost a year into his presidency, President Donald Trump has called for further investigation into the Clinton's emails.

On Tuesday, Trump appeared to suggest that Clinton's aide Huma Abedin should be imprisoned after it emerged that emails from her containing classified material were found on the computer of her husband, disgraced former congressman, Anthony Weiner. He also seemed to accuse the Justice Department of being part of the "Deep State."

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"Crooked Hillary Clinton's top aid, Huma Abedin, has been accused of disregarding basic security protocols. She put Classified Passwords into the hands of foreign agents. Remember sailors picture on submarine? Jail! Deep State Justice Dept must finally act? Also on Comey & others."

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