Riot police fired volleys of tear gas Thursday to drive back thousands of farmers chanting "Drive out the Yankees" as they tried to march on the U.S. Embassy to demand a halt to American farm imports.

Some 2,000 riot police in green combat fatigues and black, visored helmets blocked 7,000 farmers and other protesters who tried to get to the embassy in central Seoul."Drive out U.S. imperialists," and "Oppose U.S. agricultural products," protesters shouted as they marched to the beat of drums and carried hundreds of red, white and yellow flags and placards denouncing the United States.

Hundreds of protesters hurled rocks and bricks at riot police.