Two homemade bombs and a grenade exploded in separate attacks Thursday in the southern Philippines, killing a police officer and wounding five others, including a police explosives expert, officials said.

Col. Ruperto Pabustan, commander of the 602nd Infantry Brigade in North Cotabato province, said he suspected involvement in the explosives attacks by Al Qaeda-linked groups Abu Sayyaf and Jemaah Islamiyah. He said he based that opinion on the bombs' design and their locations in busy areas.

There was no evidence linking the grenade attack to the bomb attacks, officials in the autonomous, predominantly Muslim province said.

A man riding a motorcycle was seen lobbing a grenade at the guardhouse of a government compound in southern Cotabato, killing a police officer and seriously wounding three others, police said.

Almost simultaneously, two bombs went off about 50 miles away in Kidapawan, wounding a police ordnance expert and passers-by, officials said. A small one went off on a roadside near a hotel, but caused no injuries or damage, they said.

A second bomb made from a mortar shell was discovered shortly afterward by passers-by near a busy road, prompting deployment of a bomb squad, police said. As they prepared to approach the bomb, it exploded, injuring an officer and a civilian, provincial police chief Federico Dulay said.

Army troops and police had cleared the area before the explosion, possibly preventing a larger number of casualties, he said.

No one claimed responsibility for the Kidapawan blasts. Dulay said he speculated terrorist groups were involved, in part because the explosives appeared to be different from those used by extortion gangs.

"They were aimed at bringing about a deterioration in the security," he said in a telephone interview.

Dulay placed Kidapawan's 70-member police force on high alert and ordered road checkpoints and intensified street patrols. A police investigation was underway to identify the attackers.

The military is waging offensives in the region against the Abu Sayyaf, a small but violent group of Filipino extremists, and against suspected Indonesian militants on nearby Jolo island.

Kidapawan, about 570 miles south of Manila, has had several bomb attacks in recent years. Communist and Muslim guerrillas have a presence there.