Protesters grab the riot shield of a police officer as the former managed to slip past them for a rally to mark the 24th year anniversary of the termination of the U.S. military bases in the country.

Riot policemen dispersed dozens of left-wing students, who stormed past a police cordon after dawn on Wednesday and splattered red paint on the seal of the U.S. Embassy in Manila to protest the American military presence in the country.

Police arrested at least six of the approximately 50 protesters, some of whom were hit by police shields, according to witnesses and photographs. The protesters managed to slip past a police security cordon by pretending to be joggers.

The activists from the League of Filipino Students, who held up placards that read, “U.S. troops out now,” were protesting visits by American forces, warships and planes.

Vast U.S. bases were closed in the country after the Philippine Senate rejected a bid to sign new leases in 1991, but American forces were allowed back for temporary visits and joint training with Filipino troops under the 1999 Visiting Forces Agreement a few years after China took control of a disputed reef in the South China Sea off the western Philippines.

The U.S. and the Philippines, which are longtime treaty allies, signed an additional agreement last year that would allow U.S. forces to build quarters and store weapons and equipment in Philippine military bases, possibly including those facing the disputed waters.

Left-wing groups questioned the constitutionality of the agreement at the Supreme Court in a legal challenge that remains pending, hampering the accord’s enforcement.