Philippines President Gloria Arroyo on Wednesday appeared to rule out an active combat role for US troops in the fight against the country's rebels, one day after a bomb killed 21 people and injured 150 others.
President Arroyo visited the scene of Tuesday's blast
Mrs Arroyo, speaking after visiting survivors of the blast, said Philippine troops would have to do the fighting, as stipulated by the constitution.
Her comments appeared to be at odds with US hopes for a more active role in the long-standing struggle against Muslim and other rebels, some of which Washington accuses of having terrorist links with al Qaeda.
"I have drawn the line at non-combat, where I want our
soldiers to do the fighting and not their soldiers," Mrs Arroyo said.
She was speaking as confusion surrounded the Davao attack.
A man claiming to represent the radical Islamic group Abu Sayyaf said it planted the bomb.
But authorities in Manila dismissed the claim, instead blaming the Moro Islamic Liberation Front, or MILF, for the attack.
They arrested five suspected MILF rebels within hours of the blast, which exploded outside the arrivals terminal at Davao City airport on the island of Mindanao.
Amidst already high tensions in the region, another bomb ripped through a department store in the southern city of Cotabato on Wednesday, causing a small fire but no casualties, police said.
It is unknown as yet whether this bomb is connected to the attack in Davao.
Abu Sayyaf's claim of responsibility came from Hamsiraji Sali, one of the group's senior leaders, a local television network said.
He apologised to the victims and threatened more attacks.
But the BBC correspondent in Manila John McLean says the authorities have treated previous claims made by this particular leader with great scepticism.
Colonel Bonifacio Ramos, a military commander on the nearby island of Basilan, said: "This guy is lying and he is just trying to ride on the
Abu Sayyaf, which is alleged to have ties to the al-Qaeda network, is regarded as a terrorist organisation by the United States, although their main occupation is kidnapping for ransom.
US anti-terror troops were first deployed to train their Philippine counterparts last year. A small number remain in the southern town of Zamboanga.
Pentagon officials last month said a new deployment would include about 350 special forces soldiers and 400 support personnel and be targeted at the Abu Sayyaf stronghold of Jolo.
But the announcement has been criticised as premature by Philippine officials, and stoked popular resentment against US troops' presence.
An American was among the dead in the Davao explosion, but the bombers are not thought to have targeted Americans specifically.
Mindanao is mired in factional fighting, with government troops clashing regularly with four different rebel groups.
MILF forces have been on the run from central Mindanao since Ms Arroyo ordered an assault on a major stronghold in the Liguasan Marsh last month, which left nearly 200 guerrillas dead.
The airport bombing is the latest in a wave of
explosions to hit the region - including a car-bomb at Cotabato airport last month, an attack in the market town of Kabacan and a series of sabotage attacks on power transmission pylons.
President Arroyo said on Wednesday that while she remained open to a political settlement for the 25-year Muslim separatist rebellion, "for those who continue to use violence as a means to carry out their message, there is also the arm of the law."