Seoul, South Korea ? More than 4,000 anti-U.S. activists failed to break through a barricade blocking the road to a new U.S. military base.

The demonstrators, protesting the expansion plans, were met by nearly 20,000 riot police with helmets and plastic shields. No major clashes occurred. About 30 protesters were detained for throwing dirt and stones at police, and three demonstrators and two police officers suffered mild injuries, Yonhap news agency reported.

For months, activists have protested a Seoul-Washington plan to move the U.S. military headquarters based in Seoul and some other bases to Pyeongtaek. Several villages on the outskirts of Pyeongtaek, a city of 360,000, must be razed for the base construction. About 70 households have resisted moving out despite the government’s offer of financial compensation.