ZAMBOANGA, Philippines ? At least five Muslim guerrillas were killed Friday in a battle with Philippine troops on Basilan island, where two Americans and a Filipino nurse are being held hostage, a Philippine military commander said.

The firefight came a day after the Philippines and the United States opened a training exercise aimed at wiping out the Abu Sayyaf guerrillas, who have been linked to the al-Qaida terror network.

In Manila, meanwhile, two lawyers asked the Supreme Court to stop the exercise, arguing a bilateral agreement contains no provision allowing U.S. troops to be deployed “in a war zone area” like Basilan.

Philippine soldiers engaged about 20 guerrillas in a 15-minute gunfight around Maluso town on Basilan island near Zamboanga, Southern Command chief Lt. Gen. Roy Cimatu said.

“I would say that this group is the blocking force of the main Abu Sayyaf group that is holding the hostages,” Cimatu said. “If it is … probably we will have some positive developments in the near future.”

Troops recovered the body of one guerrilla, five assault rifles, personal belongings and ammunition in the village of Las Poler. The remaining guerrillas were being pursued by the marines, who suffered no injuries, Cimatu said.

“We have destroyed their perimeter defense … (while) degrading their capability in terms of strength and firepower,” he said.

The guerrillas have eluded about 7,000 soldiers deployed to Basilan since an Abu Sayyaf kidnapping spree began in May. The guerrillas still hold Christian missionaries Martin and Gracia Burnham of Wichita, Kan., and nurse Deborah Yap of Basilan.

On Thursday, U.S. troops began a six-month training exercise for Filipino soldiers that U.S. charge d’affaires Robert Fitts said will “help eliminate the terrorist parasites” threatening both countries.

The exercise will involve 660 U.S. soldiers, including 160 special forces troops.