A former Guantánamo detainee living in Uruguay has gone missing following an alleged trip to Brazil. Brazilian authorities say they have no record of Jihad Ahmed Diyab, and a national airline has called for employees to be on the alert for him.

Diyab, also known as Abu Wa’el Dhiab, was released with five other Guantánamo Bay prisoners into Uruguay in 2014 as part of a program organized by socialist President José Mujica to help President Barack Obama empty the military facility of detainees. Having staged various hunger strikes while in detention, Diyab suffers from poor health and cannot walk without crutches. He speaks very limited English and no Spanish or Portuguese, making it somewhat difficult for him to travel in the region unnoticed.

The alert, issued by Colombia’s Avianca Airlines, warned that Diyab may be using a fake Syrian, Jordanian, or Morroccan passport. It follows an admission by the government of Brazil that they have no record of the man entering the country, despite Uruguayan authorities insisting he is in Brazil.

“I don’t know if it was in an illegal manner, but he left the country,” Uruguayan Minister of the Interior Eduardo Bonomi confirmed this week. “He did not pass through any official registry.” He added that Diyab had tried to enter Brazil previously but was denied entry due to his record as a documented jihadist. Qatar also rejected him, for the same reason.

His whereabouts, Bonomi added, are now “Brazil’s problem.”

American officials are cooperating with the mission to locate Diyab. “In the broadest sense, what we are doing is working with Uruguay so that the settlement of ex-prisoners will be a success,” Brad Freden, a U.S. representative at the Montevideo embassy, told reporters last Thursday.

Some Uruguayan authorities are insisting that Diyab’s disappearance should not be cause for alarm. The Associate Press cites former Uruguayan Deputy Foreign Minister Belela Herrera as calling it “crazy” to associate Diyab with terrorism. She claims the Muslim community in Uruguay has told her he had intended to leave the country for the Muslim holy month of Ramadan, which ends Tuesday.

According to official U.S. documents, Diyab was arrested for his ties to numerous jihadi groups, including “Libyan Islamic Fighting Group (LIFG), Lashkar-e-Tayyiba (LT), Ansar al-Islam, Harakat al-Mujahidin (HUM), and Harakat ul-Jihad-i-Islami (HUJI).” He is described as “an associate of several other significant al-Qaida members.” He also received free lodging in Kabul, Afghanistan, in 2000, courtesy of the Taliban.

Diyab was detained years before al-Qaeda in Iraq evolved into the now better-known offshoot, the Islamic State, so his record does not reflect any concrete ties to ISIS.

Diyab also fashioned himself into an activist at Guantánamo and, later, in Uruguay. “Allah is just and one cannot forget that justice is the rule of all. Islam is tolerance, peace, and justice,” he said in a press conference in 2015, demanding the United States offer them salaries in Uruguay.

Diyab traveled to Argentina in 2015, his mother’s homeland. There, he insisted he was seeking ties with the long-lost Argentine side of his family, and he told reporters he was hoping to receive Argentine citizenship.

Diyab’s disappearance en route to Brazil is particularly concerning in light of next month’s Olympic Games in Rio de Janeiro, which authorities say jihadists are already planning to interrupt with terrorist attacks. Brazilian officials say they have intercepted jihadist chatter on communications applications like Telegram, stating in Portuguese their interest in attacking the games. Rio de Janeiro’s security infrastructure is in shambles due to a near-complete lack of funds that has police stations requesting locals donate toilet paper.