South Korean police said on Sunday they were holding 11 people in custody for illegally taking to the streets during an anti-US protest ahead of President George W Bush's visit to the country.
Some 1,000 protesters marched in downtown Seoul late on Saturday, according to police. No violence erupted but 13 people were held for illegally being in the streets and disrupting traffic.
Two young students were released but the other 11 were still in custody for questioning Sunday, police said.
Street protests have largely ended since South Korea secured extra health safeguards from Washington following a decision to resume imports of US beef.
Bush will visit South Korea and Thailand before attending the opening ceremony of the Olympic Games in China on August 8.