Story highlights Prisoners are transferred in the middle of the night, then taken to hospitals

Uruguay's president calls it "hospitality for humans suffering a heinous kidnapping"

The U.S. expresses gratitude to Uruguay for supporting efforts to close Guantanamo Bay

136 detainees remain at Guantanamo, the lowest number since 2002

A half-dozen men considered prisoners in the U.S. war on terror until yesterday now have a new designation -- refugees -- and a new temporary home: Uruguay.

A U.S. medical aircraft carrying the six former Guantanamo Bay detainees landed at a military base in the Uruguayan capital, Montevideo, in the middle of the night, CNN affiliate Canal 10 Uruguay reported on Sunday.

Within a few hours, a caravan of 15 to 20 vehicles, including ambulances, drove the newly freed men to hospitals.

The U.S. Defense Department confirmed the transfer Sunday and said it coordinated with the government of Uruguay to make sure the transfers took place with adequate security and with humane treatment.

"The United States is grateful to the government of Uruguay for its willingness to support ongoing U.S. efforts to close the Guantanamo Bay detention facility," the department said.

"We have offered our hospitality for humans suffering a heinous kidnapping in Guantanamo," Uruguayan President Jose Mujica wrote on his presidential website on Friday. "The unavoidable reason is humanitarian."

Four of the former detainees -- Ahmed Adnan Ahjam, Ali Hussain Shaabaan, Omar Mahmoud Faraj, and Jihad Diyab -- are Syrian nationals, while Abdul Bin Mohammed Abis Ourgy is Tunisian, and Mohammed Tahanmatan is Palestinian, Pentagon press secretary Rear Adm. John Kirby said Sunday.

Canal 10 reported that the United Nations refugee agency will be responsible for returning the released prisoners to their homes.

Their transfers to Uruguay were unanimously approved by the United States' Guantanamo Review Task Force, which represents six departments and agencies.

The review was prompted by an executive order issued by President Barack Obama shortly after his inauguration in January 2009.

Defense Secretary Chuck Hagel informed Congress of the intent to transfer the six men, the Defense Department said.

Saturday's transfers leave only 136 detainees at Guantanamo Bay, out of more than 750.

That's the lowest number of inmates at the base in Cuba since detainees started arriving in 2002.

At least seven detainees have died in custody over the years.

In Mujica's open letter, he also called for the United States to lift its embargo on Cuba and release some Cubans and Puerto Ricans he called political prisoners.