Six men held for more than a decade at the U.S. military prison at Guantanamo Bay, Cuba, were flown to Uruguay for resettlement on Sunday, the latest step in a slow-moving push by President Barack Obama's administration to close the facility.

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, U.S. officials said.

Obama promised to shut the prison when he took office nearly six years ago, citing the damage it inflicted on America's image around the world. But he has been unable to do so, partly because of obstacles posed by the U.S. Congress.