A South American airline issued a memo to its employees Monday to be on the lookout for a former Guantanamo Bay detainee who was resettled in Uruguay after being freed by the U.S. and has since vanished.

Danilo Alves, a spokesman for Colombia-based Avianca Airlines in Sao Paulo, told The Associated Press that the alert was issued internally to employees, but declined to give any more details.

The alert about Syrian native Abu Wa’el Dhiab adds to a growing mystery about his whereabouts. The Uruguayan authorities have insisted for weeks that he’s visiting neighboring Brazil and that as a refugee he is entitled to leave Uruguay. However, Brazilian authorities have said there is no record of Dhiab entering the country.

The Argentine web news portal Infobae published the alert, which warns employees that Dhiab may be using a fake passport. The image of the alert posted by Infobae said the information came from Brazil’s anti-terrorism police.

She said Dhiab had told friends in Uruguay's capital that he planned to keep to himself while spending the about-to-end Muslim holy month of Ramadan in the Uruguay-Brazil border region, where there is a Muslim community and mosques.

"He has a valid identity card, issued by the Uruguayan government, that allows him to go to other countries. He is not a fugitive from justice," Herrera told the AP over the weekend.

Dhiab is one of six former Guantanamo detainees resettled in Uruguay in late 2014.

Former Uruguay President Jose Mujica invited them as a humanitarian gesture, but for several of the men, their time in the country has been loaded with problems. They initially complained the government wasn't helping them enough and they also refused to get jobs, drawing criticism from Uruguayans.

Dhiab, who suffers several health problems related to hunger strikes he undertook while held at the U.S. military's Guantanamo base on Cuba, has been particularly vocal about his unhappiness in Uruguay.

Several weeks ago, Uruguayan media began reporting that he had left the country. Government officials said he had traveled to Brazil and insisted he had a right to do so. They said he had not broken any law and was not being sought.

However, last week the U.S. Embassy in Uruguay said American authorities were "collaborating" with Brazilian and Uruguayan authorities to locate Dhiab.

According to the Brazilian news outlet Plus55.com, he hasn’t been seen since June 6.

Dhiab had been held at Guantanamo Bay since 2002 for suspected ties to Al Qaeda. He spent 12 years at Guantanamo without being charged after his capture in Pakistan.

Guantanamo still holds 80 prisoners.

The Associated Press contributed to this report.