America's Brookings Institution placed its president, retired four-star Marine Gen. John Allen, on administrative leave Wednesday. (Getty Images)

Washington, June 14 (RHC)-- The Brookings Institution's president retired four-star Gen. John R. Allen has resigned from the organization, days after a court filing revealed evidence that he had secretly lobbied for Qatar.

Allen, the retired general who once commanded American troops in Afghanistan, said in his resignation letter that his decision is "best for all concerned at this moment," the Wall Street Journal reported.  "While I leave the institution with a heavy heart, I know it is best for all concerned at this moment," Allen said in the resignation letter.

His statement made no reference to the filings or any investigation. Brookings, a 106-year-old research center, had placed General Allen on administrative leave last Wednesday.  The Brookings Institution subsequently thanked Allen for his leadership during the pandemic.  Allen joined Brookings in 2017 after leading NATO and U.S. forces in Afghanistan. 

The decision comes after new federal court filings spell out a potential criminal case against Allen.  Prosecutors alleged that Allen worked to help Qatar influence American policy during a period of time when there was a diplomatic crisis in the Persian Gulf region.

General Allen had allegedly sent messages apparently seeking payments for work to help Qatar gain Washington’s backing in a feud with its regional rivals, Saudi Arabia and the United Arab Emirates.

Federal Bureau of Investigations Agent Babak Adib wrote in a search warrant application that there is "substantial evidence" that Allan violated the Foreign Agents Registration Act (FARA).  Qatar’s rivals had attempted to strangle Doha by cutting off diplomatic ties and blocking trade with the country.