WASHINGTON (Reuters) - The Obama administration has sent six Uighur Chinese detainees from the U.S. military prison at Guantanamo Bay, Cuba, to the Pacific island nation of Palau, an administration official and a rights group said on Saturday.

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The transfer leaves 215 detainees at the detention camp that President Barack Obama has pledged to close by January 22, although political and legal hurdles are making it difficult for his administration to meet that goal.

Palau has agreed to take up to a dozen Uighurs who come from China’s largely Muslim far-west region of Xinjiang and were captured by the U.S. government during the Afghanistan war launched after the September 11, 2001, attacks on the United States.

Four Uighurs have already been transferred earlier this year to Bermuda.

The Center for Constitutional Rights, a group based in New York that has represented many Guantanamo prisoners, said a total of six Uighurs had landed in Palau.

Three of them are clients of the center while the other three are represented by other lawyers. An administration official confirmed the detainees had been sent to Palau.

The departures occurred after the Supreme Court -- rejecting the administration’s position -- said on October 20 that it would hear an appeal by the Uighurs, who argue that they should be released in the United States.

However, Obama signed into law legislation Congress passed barring the release of any detainees from Guantanamo into the United States.

China has demanded the Uighurs be returned there but the U.S. government has said it could not do so because they would face persecution, and it has searched for months for a nation willing to accept them.

The center identified its three clients as Ahmad Tourson, Adel Noori and Abdulghappar Abdulrahman.

Palau has agreed to provide a temporary home for the three men while the United States continues to search for a country where they can be permanently resettled, the rights group said.

“President Obama has achieved a major milestone in his effort to close Guantanamo, but the prison cannot be shut down until other countries agree to resettle those detainees who are unable to return to their home countries,” J. Wells Dixon of the center said in a statement.

“There is an urgent need for countries like Australia and Germany to offer permanent refuge for not only the Uighurs temporarily resettled in Palau or still detained at Guantanamo, but also detainees from countries like Algeria, Libya and Tajikistan,” he said.

The three detainees also were represented by attorneys from the New York-based firm of Kramer Levin Naftalis & Frankel, including Eric Tirschwell.

“The men are happy at long last to be free,” Tirschwell said. “They have already begun learning English and look forward to becoming productive members of the Palau community, as the United States continues its diplomatic efforts on their behalf.”

Since Obama took office, a total of 25 detainees have been sent from Guantanamo to countries overseas and one detainee has been transferred to New York to stand trial on terrorism charges.