Brookings told staffers in an email Wednesday that the institute itself is not under investigation and that the think tank’s executive vice president, Ted Gayer, will serve as acting president.

“We have every confidence in the Brookings team’s ability to remain focused on delivering quality, independence, and impact,” the email said.

The federal investigation involving Allen has already ensnared Richard G. Olson, a former ambassador to the United Arab Emirates and Pakistan who pleaded guilty to federal charges last week, and Imaad Zuberi, a prolific political donor now serving a 12-year prison sentence on corruption charges. Several members of Congress have been interviewed as part of the investigation.

An FBI agent said in an affidavit in support of a search warrant there was “substantial evidence” that Allen had knowingly broken a foreign lobbying law, and had made false statements and withheld “incriminating” documents.

Allen’s alleged work for Qatar involved traveling to Qatar and met with the country’s top officials to offer them advice on how to influence U.S. policy, as well as promoting Qatar’s point of view to top White House officials and members of Congress, according to an FBI affidavit in support of a search warrant.

Allen, who was a senior fellow at the Brookings Institution prior to becoming president, used his official email account at the think tank for some of his Qatar-related communications, the affidavit says.

Qatar has long been one of Brookings’ biggest financial backers, though the institution says it has recently stopped taking Qatari funding.

“Brookings has strong policies in place to prohibit donors from directing research activities,” said the email to staffers Wednesday.