BREAKING: Brookings Institute president RESIGNS amid federal probe into illegal Qatari lobbying

The four-star Marine Corps general announced his departure in a letter and provided no explanation other than he was leaving with a "heavy heart," the Associated Press reports.

"I know it is best for all concerned in this moment," Allen stated in the letter.

Although General Allen has yet to be charged with a crime, the FBI has accused him of making false statements and withholding incriminating evidence with regard to his role in an illegal Qatari lobbying scheme.

"New federal court filings obtained Tuesday outlined a potential criminal case against former Marine Gen. John R. Allen, who led US and NATO forces in Afghanistan before being tapped in 2017 to lead the influential Brookings Institution," the Associated Press reports.

The investigation is wide-ranging and has already resulted in sentences against former ambassador to the UAE Richard G. Olson and well-known donor Imaad Zuberi, who is serving 12 years on corruption charges.

The FBI alleges that Allen provided a "false version of events" about his work for Qatar. Allen is also accused of failing to produce communications in response to a grand jury subpoena.

The Brookings Institute did not respond to requests for comment from the Associated Press. Recently, the institute claimed to have stopped receiving Qatari funds.

It is alleged that Allen lobbied Trump NSA H.R. McMaster to take on a friendlier stance to Qatar.

AP further reports:

"In a June 9 email to then McMaster, Allen said the Qataris were 'asking for some help' and wanted the White House or State Department to issue a statement with specific language calling on all sides of the Gulf diplomatic crisis to 'act with restraint.'

"Federal law enforcement officials say then-Secretary of State Rex Tillerson did what Allen told McMaster the Qataris wanted done two days later, issuing a statement that 'shifted away from earlier statements by the White House.' Tillerson’s statement called on other Gulf countries to 'ease the blockade against Qatar' and asked 'that there be no further escalation by the parties in the region.'"

In 2017, Allen became president of the prestigious think thank and makes more than $1 million a year, according to recent tax records.

"The integrity and objectivity of Brookings's scholarship constitute the institution's principal assets, and Brookings seeks to maintain high ethical standards in all its operations," Brookings said in a statement Sunday, according to AP.

Allen stopped taking donations from the wealthy country of Qatar in 2019, however; the Persian nation was a major financial backer of Brookings before they were cut off.