Seoul, South Korea ? After a day of pitched battles that left more than 200 people injured, South Korean forces secured the site of a future U.S. military base with water cannons, helicopters and bulldozers Thursday evening.

But the surprisingly violent clashes could set the stage for strained relations between American forces and the community where the new U.S. military headquarters will be located.

More than 3,000 South Korean soldiers and riot police, many armed with truncheons, clashed with about 1,000 demonstrators at the site in Pyeongtaek, 40 miles south of Seoul, beginning at 5 a.m. Thursday.

The protesters had barricaded themselves in a closed elementary school in an attempt to stop the clearing of the site. By nightfall, they had been evicted, the school demolished and the site roped off by 18 miles of razor-wire fencing.

The U.S. military headquarters in Seoul is expected to relocate south to the area around Pyeongtaek by 2008.