SEOUL: Activists and the occasional celebrity have gathered nearly every day in front of the Chinese Embassy for more than two weeks, sometimes scuffling with police or tearing up pictures of China's president as they protest on behalf of a group of North Koreans they say China holds.

The North Koreans' identities haven't been released by China: no ages, no names, no official descriptions of why they left their homeland. It's not even clear exactly how many China is holding, or whether some have already been sent back to North Korea, where human rights groups say their fate will be grim.

Since a South Korean lawmaker claimed last month that China planned to repatriate dozens of North Koreans rather than let them defect to the South, the issue has become an irritant in relations between Beijing and Seoul, who share strong economic ties and cooperate on regional diplomatic initiatives but who often are at odds over ways to deal with North Korea.

Beijing's Foreign Ministry has warned activists against ''turning up the heat over the issue.''

China fears a flood of people from its impoverished neighbor and ally, analysts say. Beijing says North Koreans who enter China illegally are economic migrants, not refugees or asylum seekers.

But the conservative South Korean lawmaker who sparked the protest, Park Sun-young, says China should acknowledge that they are trying to escape political repression.

''The North Korean defectors didn't flee their country to live in China. They left so they could live in South Korea. China should respect that,'' she said in a whisper in an interview with The Associated Press just before she fainted during a rally last week, following a 10-day hunger strike.She remained hospitalized Friday.

China has refused to disclose details about the North Koreans.

On Friday, Park's office said 38 are at risk of being sent back, and 10 others had already been repatriated. Park has said her information is based in part on details from other defectors in South Korea who say their family members are among those held.

The United Nations High Commissioner for Refugees said in a statement last month that it was closely following ''a group of some 25 North Koreans who were arrested in China in February.'' It did not say how it obtained the number. Other rights activists have put the number at between 30 and 40.

Citing family members, South Korean media have reported that China has already repatriated some. But Seoul's Foreign Ministry said it has received no such confirmation.

The activists are protesting a Chinese treaty with Pyongyang that requires Beijing to repatriate North Koreans who enter the country illegally.

China has forcibly returned tens of thousands of North Koreans over the past two decades, and most have been punished severely, Roberta Cohen, a human rights specialist with the Brookings Institution think tank, recently told the Congressional-Executive Commission on China.

She cited testimonies and reports gathered by the Committee for Human Rights in North Korea, a Washington-based rights group that she chairs.

The embassy rallies got a boost when South Korean actor Cha In-pyo and other celebrities began making appearances. Cha starred as a defector in ''Crossing,'' a 2008 film about North Koreans risking their lives to flee into China.

China is South Korea's largest trading partner, and the countries participate in international negotiations meant to persuade North Korea to abandon its nuclear program. But Beijing is also Pyongyang's biggest political ally and economic supporter.

Many North Koreans in China are fleeing political repression and want to live in South Korea, activists and South Korea's Unification Ministry say. But many also cross the border to find work in China and then bring money, food, medicine and tradable goods back home.

North Korea calls defectors ''human scum'' or citizens who have been kidnapped or coaxed into leaving. Its government-run website recently called the growing campaign to stop the repatriation a ''grave provocation'' that tarnishes Pyongyang's reputation.

Seoul has engaged in years of behind-the-scenes diplomacy with Beijing on North Korean migrants, but the government's stance has toughened amid the protests.

South Korean President Lee Myung-bak and other senior officials have publicly pressed China in recent weeks. South Korean Foreign Minister Kim Sung-hwan raised the issue in a recent meeting with his Chinese counterpart Yang Jiechi, but failed to win a pledge to stop the repatriation.

Kim has met with U.N. Secretary-General Ban Ki-moon during a trip to the U.S. this week and discussed the issue, Seoul's Foreign Ministry said. Kim is also expected to seek help from U.S. Secretary of State Hillary Clinton.

More than 21,000 North Korean defectors have arrived in South Korea since the end of the 1950-53 Korean War, according to Seoul's Unification Ministry. Most crossed the border between China and North Korea.