The release of four Syrians, a Tunisian and a Palestinian, who arrived in South America aboard a U.S. military transport plane, represented the largest single group to leave the internationally condemned U.S. detention camp since 2009.
President Barack Obama took office nearly six years ago promising to shut the prison, citing its damage to America's image around the world. But he has been unable to do so, partly because of obstacles posed by the U.S. Congress.
The transfer to Uruguay had been delayed for months. A move initially planned earlier this year was apparently held up by the Defense Department.
Differences over the pace of such transfers, said one U.S. official, added to friction between Defense Secretary Chuck Hagel and Obama's inner circle, culminating in Hagel's resignation last month.
The release of the six was put off again in August when Uruguay became concerned about domestic political risks in the run-up to its October's presidential election. But with the vote over, outgoing President Jose Mujica pressed ahead with accepting the men.
Upon their arrival in Montevideo, they were taken to a hospital for medical examinations, the U.S. official said.
"We are very grateful to Uruguay for this important humanitarian action," Clifford Sloan, Obama's State Department envoy on Guantanamo, who negotiated the resettlement deal in January, said in a statement.
"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."
Seven other prisoners have been transferred from Guantanamo since early November, including three to Georgia, two to Slovakia, one to Saudi Arabia and one to Kuwait.
With Sunday's release, the Guantanamo prisoner population has been whittled down to 136, informs Report citing Reuters.
The jail was opened by Obama's predecessor, George W. Bush, after the Sept. 11, 2001, attacks on the United States, to house terrorism suspects rounded up overseas. Most have been held for a decade or more without being charged or given a trial.