Jihad Ahmed Mustafa Dhiab, 43, outside his new home in Montevideo. (Joshua Parlow/The Washington Post)

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.

According to Uruguayan media, the country’s interior minister said on Thursday that while Dhiab would generally be free to make international trips, Brazilian officials had not allowed him to enter that country previously. The minister said Dhiab had left Uruguay but gave few other details.

If confirmed, the incident would intensify friction between the White House and Congress over resettlement of detainees remaining at the prison, a necessary step toward President Obama’s goal of shuttering the facility.

According to the Associated Press, another Uruguayan government official said that Dhiab traveled legally to Brazil. A spokesman for the Uruguayan embassy in Washington said he had no information on Dhiab’s status.

According to a military assessment made public by WikiLeaks, Dhiab was captured in Lahore, Pakistan, in 2002, and taken to Guantanamo Bay, Cuba. While U.S. officials initially suspected him of having links to militants, he was never charged.

Dhiab spent 12 years at the top-security prison and become one of a number of detainees who launched hunger strikes to protest their detention.

In December 2014, Dhiab and five other prisoners of Middle Eastern and North African origin were transferred to Uruguay. The resettlement deal was seen as a breakthrough for efforts to empty the prison of detainees who were seen as posing little threat.

According to the military documents, Dhiab was born in Lebanon to an Argentine mother.

While Obama still hopes to close the prison, lawmakers have repeatedly balked at accepting his plans for doing so. One of the chief reasons Republican lawmakers object is their concern about former detainees embracing militant activity after their release and their doubts about foreign nations’ ability to monitor them once they are set free.

Congress is now considering new legislation that would make it even harder for the Obama administration to resettle prisoners overseas or bring them to the United States. There are 80 prisoners remaining at Guantanamo.

Even shortly after his release, Dhiab appeared to be struggling to adjust to life in Montevideo, the Uruguayan capital. He and other detainees complained they received insufficient financial support and many of them suffered health problems.

Some of the former detainees camped out in front of the U.S. embassy to demand better conditions.

Officials did not comment on the details of the oversight arrangements for the six detainees in Uruguay.

“The decision to transfer a detainee is made only after detailed, specific conversations with the receiving country about the potential threat a detainee may pose after transfer and the measures the receiving country will take in order to sufficiently mitigate that threat, and to ensure humane treatment,” the official said.

The Obama administration is in the final stages of arranging additional detainee transfers.

Wells Dixon, a senior staff attorney at the Center for Constitutional Rights, which advocates for detainee rights, said he was skeptical that Dhiab had left Uruguay or entered Brazil “because of the obvious political motive to try and stop transfers and prevent the closure of Guantanamo.”