Cambodia deported a group of 20 Muslim asylum-seekers back to China, despite protests from the U.S. and the U.N., which rushed people to the airport in an attempt to physically prevent their expulsion.

As the Uighurs were put in a compound under constant guard in recent days, exile and rights groups grew increasingly nervous that Cambodia would give in to considerable pressure from Beijing, the Southeast Asian nation's largest foreign investor. The decision to expel them finally was announced on the eve of a visit from Chinese Vice President Xi Jinping.

Amnesty International warned the Uighurs could be tortured on their return to China, while analysts and exile groups said the deportation showed widespread problems with the refugee system at large.

The Uighurs, including two children, fled after ethnic rioting in July and slipped out of the country with the help of a secret missionary network in China. Their role in the rioting, China's worst communal violence in decades, remains unclear.

But China called them criminals, and Cambodia said it was deporting them because they had entered the country illegally. China's Foreign Ministry had no immediate comment Saturday night.

China has handed down at least 17 death sentences _ mostly to Uighurs _ over the summer violence between the ethnic minority and the majority Han Chinese. Exile groups say Uighurs have been rounded up in mass detentions since the rioting. Uighurs also complain the Chinese government has long restricted their rights, particularly clamping down on their practice of Islam.

Some countries have refused to send Uighurs _ such as those released from U.S. detention at Guantanamo Bay in Cuba _ back to China over concerns about retribution and abuse.

The U.S., the U.N. and several rights groups urged Cambodia not to deport the group, which, according to Interior Ministry spokesman Lt. Gen. Khieu Sopheak, left Phnom Penh International Airport on a special plane sent from China.

A spokeswoman for the United Nations High Commissioner for Refugees said it had not finished evaluating the Uighurs for refugee status and that expelling them was a "grave breach of international refugee law."

"I think we went to extraordinary lengths to prevent deportation. We had people prepared to try to physically prevent the deportation if it had taken place at the civilian side of the airport," said Kitty McKinsey, spokeswoman for the agency in Bangkok. The plane, however, left from the airport's military area.

The agency's high commissioner, Antonio Guterres, tried to speak to Prime Minister Hun Sen on the phone but was not successful, McKinsey added. She said the refugee agency is preparing a protest to the Cambodian government.