Street protests, likely led by the vice president, and a legal challenge seem certain in the former American colony, where the Supreme Court already had ruled that U.S. troops only can shoot in self-defense and the constitution prohibits the presence of foreign military facilities and troops unless covered by treaty.
"I am categorically saying that anything that they say that contradicts the constitution and the laws will not materialize," Defense Secretary Angelo Reyes 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."
Earlier, officials announced that in a major expansion of American military involvement in the Philippines, hundreds of U.S. special operations troops will soon take frontline combat roles against Abu Sayyaf rebels.
President Gloria Macapagal Arroyo did not comment, but said last year that she believed a combat role for U.S. troops in the Philippines was legal.
Unlike previous arrangements in which U.S. troops played advisory roles out of the line of fire, the American and Philippine governments agreed to place U.S. troops alongside Philippine soldiers in direct combat, defense officials said Thursday. They spoke on condition of anonymity.
The joint offensive is expected to start in March, with the exact date to be determined by the Manila government.
About 350 U.S. special operations forces, mostly Army Green Berets, will be involved in the offensive in the Sulu Archipelago, with much of the effort focused on the island of Jolo, the officials said. They will be supported by about 400 more U.S. troops based to the north in the port city of Zamboanga.
It was not immediately clear how many Philippine forces would be involved in the offensive.
Reyes said he planned to fly to Washington on Sunday for talks with Defense Secretary Donald Rumsfeld on "defense and security-related issues of mutual interest." He said the trip had been scheduled before the controversy over U.S. involvement in combat.
In addition to the U.S. special operations forces and the support personnel, a team of about 1,000 Marines aboard Navy ships off the coast of the Sulu Archipelago will be available to respond on short notice with air power, logistics help and medical aid, the U.S. officials said.
The Marines are part of the Okinawa-based 31st Marine Expeditionary Unit, and their lead ship is the USS Essex, based at Sasebo, Japan.
U.S. officials have said in recent days that they have new information showing a stronger link than previously believed between the Philippine rebels and other international terrorist groups.
The government of President Arroyo said Monday that she had approved joint training with U.S. forces on Jolo, where some Abu Sayyaf rebels fled after the previous U.S.-Filipino effort last year to root them out of Basilan island, to the north of Jolo.
U.S. officials said the March offensive would go well beyond training to include direct combat roles for U.S. forces.
The purpose, one official said, is to "disrupt and defeat the Abu Sayyaf group." He said the effort had no time limit and would continue as long as both governments agreed it was needed.
There are believed to be several hundred Abu Sayyaf rebels in the Philippines. Early this month the Philippine military announced it had greatly underestimated the number of Abu Sayyaf and warned it would take a long time to wipe them out.
A Department of National Defense report submitted to the Philippine Congress late last year placed their strength at 250, down from 800 in 2001. But Chief of Staff Gen. Dionisio Santiago acknowledged Feb. 5 that a recheck of military documents and figures showed a number closer to 500 — most on the impoverished island of Jolo.
Several terrorist groups, some with suspected links to al Qaeda such as the Islamic extremist network Jemaah Islamiyah, operate in the Philippines and there have been a series of deadly bombings, kidnappings and other attacks against both government and civilian targets. An Oct. 2 incident blamed on Abu Sayyaf killed three people, including a U.S. Green Beret in Zamboanga.
Pentagon officials say investigations following some of those attacks have turned up information indicating the link between the Abu Sayyaf and the Jemaah Islamiyah of Indonesia may be stronger than earlier believed.
There have been at least six violent incidents this week.
Friday saw two bombs explode in front of a mall in the country's south. The two 60 mm mortar rounds with timing devices were attached to the exhaust pipes of two cars parked in front of Koronadal Commercial Center mall.
Police Supt. Romeo Rufino, the South Cotabato provincial police chief, said Koronadal city police received an anonymous call claiming a bomb would explode in "a few minutes." He said police were deployed around the city, including inside and outside the mall, but they failed to find the explosives. The explosions came 30 minutes after the call.
The mall was immediately closed as people ran away in panic. Police ordered drivers of cars parked adjacent to the bombed vehicles not to leave so their cars could be inspected. The owners of the two bombed cars identified themselves to the police, claiming they were not involved.
The injured included a 32-year-old woman, a bus conductor and another man who police said they suspected was the bomber. One of the man's arms was blown off.
Provincial Gov. Daisy Avance Fuentes said the bombings could be related to fighting in central Mindanao island last week between government troops and the Moro Islamic Liberation Front that officials say left more than 160 people dead.
The MILF and Abu Sayyaf are both splinter groups from the larger Moro National Liberation Front. All three groups at one time or another have fought for the creation of a separate Muslim state in the southern Philippines.