Riot police charged into crowds of radical students, who hurled firebombs and screamed "American troops get out!" as they tried to march through Seoul to demand the removal of U.S. troops.

Several troopers were set on fire in Sunday's protest as the bombs exploded in balls of orange flame. Armored vans sprayed tear gas at the protesters, and police had to charge three times to block them from marching through the city.Police officials had no immediate word on arrests or injuries. They said 10,000 police were deployed across Seoul to block the protest.

The violence Sunday began when about 6,000 labor union activists and radical students tried to march to the city center following separate rallies.