The United States says it is "deeply troubled" by reports China is involuntarily returning North Korean refugees to their home country.

The State Department said in a report to Congress Friday that China reportedly detained and forcibly returned several thousand North Korean refugees last year.

The report says that refugees who return to North Korea often face serious abuses, including possible torture and execution.

It also says China's treatment of North Korean refugees violates U.N. rules.

China and North Korea have a treaty covering the return of North Koreans, who Beijing regards as illegal immigrants and not refugees.

Human rights groups believe some 300,000 North Koreans have fled to China to escape poverty and persecution.