MANILA, Philippines — Philippine officials denied Friday that an agreement has been reached with Washington to allow U.S. troops to engage in offensives against Muslim extremists in the southern Philippines.

U.S. defence officials in Washington said an arrangement has been agreed upon by the two governments that will place about 350 U.S. special operations troops in direct combat roles targeting the Abu Sayyaf group on southern Jolo island.

They said the plan would include a backup force of 1,000 U.S. Marines on several ships off Jolo to respond on short notice with air power, logistics help and medical aid.

Philippine Defence Secretary Angelo Reyes dismissed the statements by the unidentified U.S. officials as leaks "I'd rather not comment on."

"I am categorically saying that anything that they say that contradicts the constitution and the laws will not materialize," he said.

Pressed on whether it was possible for U.S. troops to have combat roles in the country, he replied, "That is a matter for lawyers to decide."

He said "ongoing discussions" were continuing on details of a counterterrorism exercise similar to the six-month maneuvers on southern Basilan island last year that was designed to help the Philippine military wipe out the Abu Sayyaf.

U.S. military affairs are a sensitive political issue in this former American colony whose constitution prohibits the presence of foreign military facilities and troops unless covered by a treaty approved by the Senate.

President Gloria Macapagal Arroyo's chief of staff, Rigoberto Tiglao, said the U.S. officials were "sadly misinformed" about what foreign troops are legally allowed to do in the Philippines.

Foreign Secretary Blas Ople said the exercise to be held on Jolo this year will "still basically be a training exercise."

He said the "substance" of the terms of reference governing last year's drills will not change.

Those rules allowed U.S. troops to accompany Filipino soldiers into combat zones but authorized them to shoot only in self-defence. There was only one instance when U.S. soldiers had to shoot back, when a Marine security detail on a road project on Basilan was fired upon by suspected Abu Sayyaf guerrillas.

U.S. soldiers also came close to the fighting when they helped evacuate Filipino soldiers wounded in clashes, and they provided surveillance and air support for a clash at sea in which Philippine forces said they killed several Abu Sayyaf members, including one of the group's top leaders.

The Abu Sayyaf group has kidnapped at least four Americans and killed one of them in captivity. Another was killed during a rescue operation last year. The group also was blamed for a bombing that killed an U.S. Green Beret and two Filipinos late last year. It has been loosely linked to al-Qaida and is on a U.S. list of foreign terrorist groups.

Vice President Teofisto Guingona, who opposed last year's exercise, said foreign countries should follow the Philippine constitution "no matter how powerful they are."

Senator Manuel Villar, chairman of the Senate Foreign Relations Committee, also opposed combat roles for U.S. troops.

"Terrorism is a global concern ... but we should stick to training and not allow foreign troops to fight our own battles or enemies," he said.