China voiced anger Thursday over the transfer of three Uighurs from the US military prison in Guantanamo Bay to Slovakia, branding them "terrorists" who will pose a threat to their new home.

The trio were freed earlier this week as part of Washington's efforts to close the jail, and were the last of 22 Uighurs to be held in the prison, with the others being resettled in six countries including Albania, Bermuda, El Salvador, Palau, and Switzerland.

Beijing had previously protested about the release of the men, who it says have links with the East Turkestan Islamic Movement (ETIM), which the United Nations lists as a terrorist group and which China accuses of having separatist aims in Xinjiang.

"We are firmly opposed to the US transfer of these suspects to a third country, and we are also opposed to any other countries' acceptance of them," foreign ministry spokesman Qin Gang told reporters in Beijing Thursday.

"The aforementioned suspects are members of the East Turkestan Islamic Movement, which is a terrorist organisation designated by the UN Security Council. Therefore, these prisoners are terrorists.

"They not only pose a threat to the national security of China but also will pose a threat to the security of the recipient country."

The three had been cleared for release from Guantanamo in 2008 but Washington refused to return them to China because of the potential consequences, and had struggled to find a third country to take them in amid protests from Beijing.

Campaign groups regularly complain of rights abuses against mainly Muslim Uighurs, the largest ethnic group in Xinjiang, by the authorities and dismiss claims of terrorism and separatism as an excuse by Beijing to justify religious and security restrictions.