WASHINGTON — The U.S. government said Sunday that six detainees from Guantanamo Bay have been sent to Uruguay for resettlement, the first time prisoners from the infamous facility have been transferred to South America. The release brings the total number of prisoners held at Guantanamo to 136, down from a one-time high of nearly 800.

Officials told NBC News the men departed Guantanamo on Saturday morning and arrived in Uruguay late that night. When detainees are transferred, the U.S. government is given assurances that the men will be treated humanely, but they are not imprisoned in their new home countries. Even more releases are expected before the end of this year, according to an administration official.

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The Pentagon on Sunday identified those released as Ahmed Adnan Ahjam, Ali Hussain Shaabaan, Omar Mahmoud Faraj, Abdul Bin Mohammed Abis Ourgy, Mohammed Tahanmatan, and Jihad Diyab. Four of the men have Syrian citizenship, while the others are from Tunisia and Palestine, according to Pentagon records.

Their transfer has been in the works since early this year and it was something the President of Uruguay openly discussed when he visited the U.S. in May. The six detainees had been held for more than 12 years, according to The Associated Press.

The release comes amid efforts to step up the pace of transfers in light of President Barack Obama's efforts to close the facility. Earlier this month, outgoing House Armed Services Committee Chairman Buck McKeon (R-CA) expressed hesitance over the increased pace of releases. "What the Obama Administration is doing is dangerous and, frankly, reckless. They have chosen many times to put politics above national security," he said.

Clifford Sloan, special envoy for Guantanamo Closure at the State Department, said Sunday the U.S. was grateful to Uruguay for offering a home for the detainees.

"The support we are receiving from our friends and allies is critical to achieving our shared goal of closing Guantanamo, and this transfer is a major milestone in our efforts to close the facility," he said in a statement.

— The Associated Press contributed to this report.