Relations between South Korea and China are strained after Beijing on Tuesday said it is sending 20 North Korean defectors back to their country after arresting them late last month, despite urgent requests from South Korea not to send them to almost certain internment in a gulag, torture or death in the North.

But the South Korean government is under internal pressure for failing to do its Constitutional duty to protect them. Under the Constitution, all North Koreans are automatically South Korean citizens.

Chinese authorities recently cracked down on North Korean defectors in its three northeastern provinces and apparently arrested scores in Shenyang. A South Korean group helping defectors found out about what it said were 35 arrests and appealed to the media to prevent them from being sent back to the North. The ruling Grand National Party in an emergency meeting demanded that Beijing halt the repatriations, and the Foreign Ministry dispatched an official to speak with Chinese authorities, but to no avail.

The handling of North Korean defectors has put an increasing strain on South Korea's relations with China after the number of defectors surged in the wake of a famine in North Korea in the 1990s.

One incident was the repatriation of seven North Korean defectors from Russia, who had been caught after crossing a border from China. Russia sent back them to China, and Beijing initially promised to treat them based on humanitarian principles but ended up repatriating them to North Korea, even though they were granted refugee status by the UN Human Rights Commission. The incident has been considered one of Seoul's heaviest diplomatic failures.

Seoul has continuously demanded that Beijing stop repatriation of North Koreans, citing the torture and execution they may face once they are sent back. But China usually waits until global attention wanes before sending them back to the North. This pattern has persisted for the last decade.

Bejing says it takes domestic law, international law and humanitarian principles into consideration in dealing with defectors. Humanitarian principle usually prevail in areas where there is a South Korean embassy or consulate where the defectors can shelter, and they are then quietly allowed to go to South Korea. But those captured elsewhere are sent back to the North according to Chinese laws and agreements with North Korea.

But in sending them back, China violates its obliga tions as a signatory to the UN Refugee Convention, which prohibits sending refugees back to their home country if there is a threat to their lives or freedom.

Grand National Party floor leader Hwang Woo-yea said, "Forced repatriation of North Korean refugees is a clear violation of the UN convention and we must do everything we can to stop this."