John R. Allen, a retired four-star Marine general who was the president of the Brookings Institution, had been accused of secretly lobbying for the government of Qatar.

John R. Allen, a retired four-star Marine general who was the president of the Brookings Institution, had been accused of secretly lobbying for the government of Qatar. federal prosecutors have closed an investigation into whether he secretly lobbied for the government of Qatar and that no criminal charges will be brought against him in the case The F.B.I. agent’s application provided a detailed account of a period in June 2017, when General Allen met frequently with Richard G. Olson, a former U.S. ambassador to the United Arab Emirates and Pakistan, and Imaad Zuberi, a businessman with ties in the Middle East. General Allen traveled to Doha, Qatar, during that period.

Federal prosecutors have signaled a particular interest in potential violations involving Persian Gulf nations, which have developed close ties to business and political figures in the United States. According to the F.B.I. agent’s application, General Allen was recruited by Mr. Olson and Mr. Zuberi to help defuse a diplomatic crisis between Qatar and its Persian Gulf neighbors — and the former general saw the moneymaking potential for his involvement. The F.B.I. agent’s application said that General Allen had agreed to travel to Doha at Mr. Zuberi’s expense and negotiated a payment of $20,000, which he referred to as a “speaker’s fee.”

“General Allen has never acted as an agent of the Qatari government,” Mr. Phillips said. “He never had an agreement — written or oral — with Qatar or any other Qatar-related individual or entity. Neither General Allen nor any entity with which he was or is affiliated ever received fees — directly or indirectly — from the Qatari government for his efforts. Brookings never received a contribution from Qatar or any Qatari government-related entities or individuals in connection with General Allen’s activities.”

Federal law requires that anyone lobbying for a foreign government register with the Justice Department, and in recent years the department has tried to crack down on suspected violations of the Foreign Agents Registration Act, or FARA.