[US troops] will not engage in combat, period

National Security Adviser Roilo Golez

She had convened the national security council after Vice-President Teofisto Guingona said he doubted the legality of the deployment of more than 600 US soldiers.

After the meeting, Mr Guingona said he would not resign over the matter, despite his reservations.

But outside the presidential palace, riot police clashed with dozens of demonstrators, who had burned President Arroyo's effigy in protest.

The Philippine constitution bans foreign troops from operating in the country's territory without a formal treaty.

Troops arrive

Last week an undisclosed number of US troops flew in to the southern island of Basilan ahead of what are described as joint military exercises.

The US military says soldiers will provide training and advice to the Philippine authorities but will not engage Abu Sayyaf forces unless attacked.

But many Filipinos suspect the US wants to open a second front in its war on terrorism, and there has been speculation that the joint exercises are a cover for a US operation to rescue an American couple kidnapped by the Abu Sayyaf.

US hostages

Many Filipinos oppose US involvement

Martin and Gracia Burnham, from Kansas, were seized from a luxury tourist resort last May. It is thought they are being held in jungle on Basilan island, along with a Filipino nurse.

Our correspondent in Manila, John McLean, says people's suspicions about the US have been reinforced because the training exercises will include live firing exercises on Basilan.

The Abu Sayyaf is made up of a few hundred fighters who say they are fighting for independence for the country's Muslim minority.

However, their main activity is kidnapping for profit.