A former Guantanamo Bay prisoner transferred to Uruguay in 2014 has vanished and is believed to have left the country under uncertain circumstances, U.S. officials said.

Law enforcement is now searching for the former detainee, Syrian national Jihad Ahmed Mustafa Dhiab, in Brazil, a U.S. official said.

“We are coordinating with officials in Brazil and Uruguay to determine his whereabouts,” the official said, speaking on the condition of anonymity to discuss a sensitive incident.

While the Obama administration declined to comment publicly about the case, officials believe that Dhiab may have crossed into Brazil without documents that would allow him to enter that country legally.