THREE soldiers have been killed in an attack by al Qaeda-linked Islamic militants in the southern Philippines, a military spokesman said on Sunday.

The three were members of the army's intelligence unit on the southern island of Basilan and had left their barracks to buy food when they were attacked by Abu Sayyaf gunmen on Saturday, Captain Alberto Caber said.

"They were aboard a motorcycle when attacked from behind by men also riding motorcycles," Caber told reporters.

The soldiers sustained multiple gunshot wounds and were pronounced dead upon arrival at a local hospital, he said.

Caber blamed Abu Sayyaf for the attack, saying that it could be trying to goad the military into attacks on the eve of the expected signing of a peace agreement with another Muslim group.

"This is the work of the Abu Sayyaf to spoil the signing" of the peace agreement with the Moro Islamic Liberation Front (MILF) in Manila on Monday, he said.

The 12,000-strong MILF is to sign a "framework agreement" with the government laying down the blueprint for the creation of an autonomous region by 2016.

Caber said that the Abu Sayyaf apparently feared that once the pact is signed, the MILF would actively help the military hunt them down in the jungles of Basilan.

The Abu Sayyaf is blamed for the country's worst terrorist attacks, including a 2004 ferry bombing that killed over 100 in Manila Bay, as well as kidnappings of foreign tourists and missionaries over the past decade.

The group is on the US government's list of active foreign terrorist organizations, and 600 American soldiers rotate in the south yearly to help local counterparts combat it.