"U.S. forces are not involved in combat operations," U.S. Embassy spokeswoman Rebecca Thompson said in a statement today. She said American troops were on temporary deployment at the invitation of the Philippine military and government.

The left-wing group Bayan, which has led anti-U.S. protests, and former Senate President Jovito Salonga have asked the Supreme Court to reconsider a decision to uphold the Visiting Forces Agreement, which governs the conduct of U.S. troops. They say the agreement infringes on Philippine sovereignty and violates a constitutional prohibition of foreign military bases.

Executive Secretary Eduardo Ermita, President Gloria Macapagal Arroyo's top Cabinet aide, defended the 1998 agreement, saying it was key to the defense of the Philippines.

The U.S. military presence is a sensitive issue in the former American colony. In 1991, the Philippine Senate under Salonga voted to close down two major U.S. bases.

Two US soldiers and a Filipino marine have been killed in a landmine blast on the southern Philippine island of Jolo, a Philippine army spokesman has said.

Two other Filipino soldiers were also wounded in the explosion, which hit their vehicle near the town of Indanan.