The Philippine Supreme Court has ordered President Gloria Arroyo's government to justify its decision to let U.S. troops participate in the campaign against Muslim guerrillas.
The U.S. soldiers are taking part in joint exercises aimed at wiping out Abu Sayyaf rebels in the southern Philippines. Up to 600 American troops will ultimately be involved.
The court order was in response to a petition filed last week by two lawyers who say the U.S. presence violates the Philippine constitution, a view shared by many opposition politicians.
The Americans are to participate in patrols and help advise Philippine forces. But Ms. Arroyo says they will not be directly involved in combat and will use their weapons only in self-defense.
Abu Sayyaf is holding two Americans and a Philippine nurse hostage, and U.S. officials have said the group has links with Osama bin-Laden's al-Qaida terrorist network.