Protesters hurled firebombs into U.S. Army headquarters Friday in an escalating anti-American campaign, U.S. and South Korean authorities said. No damage was reported.

The attack followed an outburst of anti-U.S. sentiment spurred by incidents involving American athletes and news media during the Olympics. The Games, which began Sept. 17, end Sunday.Police and U.S. military authorities said a band of youths, believed to be radical students, tossed firebombs over a wall into a motor pool at the headquarters of the 8th U.S. Army near central Seoul. Police said nine people involved in the attack fled.

Newspapers and Yonhap, the South Korean news agency, said the attack involved at least 20 youths who threw at least four firebombs from an elevated walkway and left 15 more behind.

It was the second firebomb attack on U.S. armed forces' facilities this year, a U.S. military spokesman said. A window was broken in the first attack, the spokesman said without elaborating.