SEOUL, South Korea — China plans to shut down all bridges linked to North Korea during next month's Olympics as part of its efforts to prevent North Koreans from crossing into China, a news report said Monday.

China has also demanded that North Koreans working in China leave the country, Yonhap news agency reported, citing unnamed diplomatic sources.

A Chinese Foreign Ministry official identified only by his surname Shang said he has never heard of such a report.

Officials at the North's embassy in Beijing were not immediately available for comment.

A growing number of North Koreans cross into China in search of food and to avoid political oppression and many seek eventual asylum in South Korea. Activists claim tens of thousands of North Koreans live in hiding in China, where they face forced repatriation to their impoverished homeland if caught.

As a key ideological ally of the North, China views North Korean defectors as "economic migrants," not refugees, and is obligated to send them back under a bilateral treaty.

But China has allowed those involved in high-profile cases to travel to South Korea, usually via a third country, to avoid international opprobrium.

More than 13,500 North Koreans have arrived in the South since the Korean War, according to South Korea's Unification Ministry. The war ended with a 1953 cease-fire that has never been replaced with a peace treaty.