A fire at the main U.S. military base in South Korea injured three South Korean workers early Thursday and destroyed four buildings, police said. A woman was being questioned on suspicion of starting the fire in an attack against the United States.

The workers were treated for second-degree burns, said an official at the Yongsan police station who declined to give his name, citing official policy.

The fire at the Yongsan Garrison in central Seoul raged for nearly four hours before it was extinguished at 5:30 a.m. A storage house was among the buildings destroyed.

Police were questioning a 57-year-old South Korean woman found on the base. It was unclear how the suspect — who has a record of treatment for mental disease — managed to enter the base when all the gates were locked, police said.

The Yonhap news agency quoted the woman as telling police she started the fire with a lighter to punish the U.S. "for its terrorist activities."

The U.S. base is set in coming years to move to a new location in Pyeongtaek, 40 miles south of the capital, and the land to be turned back over to South Korea.

About 29,500 U.S. troops are stationed in South Korea as a legacy of the 1950-53 Korean War. The number is set to decline to 25,000 by 2008 as part of the Pentagon's worldwide realignment of its forces.