WASHINGTON — In what the Pentagon called a "significant milestone" in the effort to close the prison at Guantánamo Bay, Cuba, the military announced on Tuesday that the United States had transferred three Chinese detainees to Slovakia.

The three were the last of 22 ethnic Uighurs from China who were captured in Afghanistan after the American invasion in 2001 and brought to Guantánamo. Although the military decided that they were not at war with the United States and should be released — and a judge ordered them freed in 2008 — they remained stranded because of difficulties in finding a safe and agreeable place to send them.

"The United States is grateful to the government of Slovakia for this humanitarian gesture and its willingness to support U.S. efforts to close the Guantánamo Bay detention facility," said Rear Adm. John Kirby, the Pentagon press secretary. "The United States coordinated with the government of Slovakia to ensure the transfer took place in accordance with appropriate security and humane treatment measures."

With these transfers, a total of nine detainees have departed Guantánamo in December, and 11 since last summer, when President Obama revived his stagnant efforts to close the prison by appointing Cliff Sloan as a new State Department envoy for the effort to winnow down its population of low-level detainees. There are 155 prisoners remaining at Guantánamo. Of those, about half have long been approved for transfer if security conditions can be met in the receiving country, the bulk of whom are Yemenis.

In a statement, Mr. Sloan said, "We deeply appreciate Slovakia's humanitarian assistance in accepting these three individuals from Guantánamo who were in need of resettlement," and he portrayed the relationship between the United States and Slovakia as strong and close.

"All 22 Uighurs from Guantánamo now have been resettled to six different countries, and these three resettlements are an important step in implementing President Obama's directive to close the Guantánamo detention facility," he said.

The Uighurs have long served as a particularly high profile symbol for opponents of the Guantánamo policy. Leaked dossiers for the three detainees sent to Slovakia — Yusef Abbas, Hajiakbar Abdulghupur, and Saidullah Khalik — say that at least as early as 2003, the military had determined they were "not affiliated with Al Qaeda or a Taliban leader" and should be released.

But the United States could not repatriate the Uighurs because the Chinese government has a history of mistreating Uighurs as it deals with ethnic unrest in its vast Central Asian border region of Xinjiang, where Uighurs are the largest ethnic group; the American military believed some of the Uighurs had received weapons training at a camp in Afghanistan run by a separatist Uighur group. Other countries were reluctant to take them, in part because of Chinese diplomatic pressure.

In 2006, the Bush administration sent five of the Uighurs to Albania, but destinations for the rest remained elusive. In 2008, a federal district court judge ordered the remaining 17 be brought into the United States. But in February 2009, the federal appeals court for the District of Columbia overturned that ruling, saying the judiciary could not order the executive branch to admit a foreigner into the country. The Supreme Court declined to review the matter.

Meanwhile, in the spring of 2009, the Obama administration nearly resettled two of the men in the care of a Uighur community in Northern Virginia, as a test case and in hopes of inducing other countries to take detainees. But a congressional backlash scuttled the plan and helped foster an atmosphere in which lawmakers imposed transfer restrictions on detainees.

Greg Craig, who was Mr. Obama's White House counsel in the first year of the administration and was closely involved in efforts to resolve the Uighurs' fate, celebrated the departure of the last Uighurs from Guantánamo.

"From the beginning, we knew that one test of our determination to close Guantánamo would be measured by what happened to the Uighurs," Mr. Craig said of the final transfers. "That the last of the Uighurs has now left Guantánamo is an important milestone. They didn't belong there in the first place."

Amid intense lobbying by the United States, in 2009 four were sent to Bermuda and six to Palau, and in 2010 two went to Switzerland. In a twist, however, releasing the rest became a problem because the remaining five detainees refused offers to go to certain countries, extending their imprisonment for years.

All five rejected offers to go to Palau or the Maldives, officials said. Last year, El Salvador offered to take them in, and two accepted that offer while the final three are said to have rejected that opportunity, too, and held out for something they liked better.

Last summer, according to an American official familiar with the matter, Costa Rica offered to take the remaining three, and the deal advanced enough that in September the Obama administration notified Congress that it intended to transfer them. But China pressured Costa Rica to withdraw its offer, and it did so.

Their transfers to Slovakia, which the military said were voluntary, come days after Mr. Obama signed into law a new version of the annual National Defense Authorization Act. In that law, Congress extended restrictions on transferring Guantánamo detainees into the United States, but relaxed some restrictions on transferring them to other countries.

In a statement he issued when he signed the bill on Dec. 26, Mr. Obama reiterated his belief that closing the Guantánamo prison was a good policy and suggested vaguely that some of the transfer restrictions might be unconstitutional constraints on his powers, echoing assertions he has made when signing previous versions of the law.

"The detention facility at Guantánamo continues to impose significant costs on the American people," Mr. Obama said. "I am encouraged that this act provides the executive greater flexibility to transfer Guantánamo detainees abroad, and look forward to working with the Congress to take the additional steps needed to close the facility."