BEIJING (REUTERS).- Chinese police have prevented artist Ai Weiwei from traveling to South Korea, he said on Friday, linking it to a crackdown on dissidents ahead of the formal awarding of the Nobel Peace Prize to a prominent rights activist.

Ai had been due to board a flight from Beijing to South Korea on Thursday evening, when police presented him with a piece of paper saying he was not allowed to leave China on grounds of endangering security.

"They said my leaving the country would threaten national security. They were very polite, and said that in accordance with the law, I could not leave ... It's really silly," Ai told Reuters by telephone.

"I think there's a direct connection with next week's Nobel Peace Prize award," he added. "The Chinese government is very upset about this."

Chinese police could not immediately be reached for comment.

This year's prize to jailed Chinese dissident Liu Xiaobo is due to be formally awarded next Friday in Norway's capital Oslo.

China, furious that the award has gone to a man it labels a criminal and a subversive, has detained a number of dissidents and prevented many others from leaving the country, apparently fearful some will try and make their way to Norway.

China stopped Liu's lawyer Mo Shaoping last month from boarding a plane to London for a conference.

"Police and border control officials are increasing their efforts to bar prominent members of Chinese civil society from traveling internationally as the Nobel Peace Prize ceremony approaches," activist group Chinese Human Rights Defenders said.

Ai is one of China's most famous contemporary artists. His career spans protests for artistic freedom in 1979, provocative works in the 1990s and a hand in designing the Bird's Nest stadium for the 2008 Beijing Olympics.

Ai's public comments, activities and art are some of the loudest, most flagrantly defiant forms of speech in China today, where government controls on the Internet and traditional media constrain civil society.

Ai has never been formally arrested, despite his occasional brushes with the law. He was placed under house arrest last month in connection with an argument with the government over the planned demolition of his studio in Shanghai.

(Reporting by Ben Blanchard; Editing by Sanjeev Miglani)