WASHINGTON — The disappearance of a former Guantánamo Bay prisoner who was transferred to Uruguay is sharpening debate here over the wartime prison, even as a House committee prepares to hold an oversight hearing on Thursday about the Obama administration’s policy on releasing detainees to other countries.

The former detainee, Jihad Diyab, is a Syrian who was among six lower-level detainees resettled in Uruguay in December 2014. Early last month, he told several people that he was going on a religious retreat that would last beyond the Muslim holy month of Ramadan and into next week — and that he would be unreachable by telephone or email.

Since then, some Uruguayan officials have said they lost track of him, and suggested that he may have crossed the largely unguarded border into Brazil. Heightening tensions, a Colombia-based airline asked its employees to alert authorities if they came into contact with him.

On Wednesday, Alexandre Moraes, Brazil’s justice minister, told reporters that “there is no sign” he was in Brazil. In Uruguay, Fernando Gil, a spokesman for the Interior Ministry, said Uruguayan authorities were not hunting for him. “As far as Uruguay is concerned, the person is here in the country,” Mr. Gil said.