U.S. intelligence officials have told Congress that Guantanamo Bay detainees who were “recently” released are already trying to rejoin terrorist groups, according to a key Republican lawmaker.

“The committee has just received a troubling new report from the intelligence community indicating that former detainees recently transferred out of Guantanamo Bay by your administration are attempting to return to terrorism,” House Foreign Affairs Committee chairman Ed Royce, R-Calif., wrote Tuesday in a letter to the White House. “Even more concerning, this report indicates that the country to which these detainees were transferred has little ability to prevent their return to the battlefield — a fact known to your Administration prior to their transfer.”