Many Filipinos oppose US involvement

There is a growing debate in the Philippines over the deployment there of the US forces - a total of about 660 are expected to arrive.

The Philippines constitution bars foreign troops from operating in the country except for training purposes.

President Gloria Arroyo defended the move on US television, saying the American troops were in the Philippines to provide training, and not to fight Abu Sayyaf Muslim rebels linked to Osama bin Laden.

US Defence Secretary Donald Rumsfeld said earlier this week as many as 250 US troops were already in the Philippines, but he said they were there for "logistics purposes" only.

Deployment doubts

But the president of the Philippine senate, Franklin Drilon, on Thursday called for an inquiry into the exercises to determine whether the American presence is unconstitutional.

The rebels are holding two US hostages

The US is also a former colonial power, and nationalist sentiment in the country is opposed to US involvement.

John McLean, the BBC's Manila correspondent, says many Filipinos suspect the US wants to open a second front in its war on terrorism.

He says there is speculation that the joint exercises are a cover for a US operation to rescue an American couple kidnapped by the Abu Sayyaf.

US hostages

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 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.