Photo/Illutration A photo provided by the Philippine Red Cross shows troopers securing an area after two explosions struck the town of Jolo, in the Sulu province of the southern Philippines on Aug. 24. (AP Photo)

 MANILA--Bombs exploded in a southern Philippine town Monday, killing at least five soldiers and wounding 17 other military personnel and civilians despite extra tight security because of threats from Abu Sayyaf militants.

Regional military spokesman Capt. Rex Payot and police said the blast damaged a food store, a computer shop and two army trucks at noon in Jolo town in Sulu province. An initial report said the first bomb was attached to a parked motorcycle.

A second blast was heard in the area shortly after but it was not immediately clear if it caused more casualties or damage in the downtown area, which has been cordoned off by troops and police.

Two military officers said five army soldiers were killed in the initial blast but did not provide other details. An initial picture showed soldiers carrying a man from the scene of the explosion near an army truck. Another blast victim lay on the road.

There was no immediate claim of responsibility for the attack, but Abu Sayyaf militants have been blamed for most deadly bombings in Sulu and outlying provinces, where they have a presence.

The military has been waging a months-long offensive against the Abu Sayyaf, a small but violent group aligned with the Islamic State group and blacklisted by the United States and the Philippines for past bombings, ransom kidnappings and beheadings.

The number of its armed fighters have dwindled to a few hundred in recent years due to battle setbacks and surrenders, including a key commander, Abduljihad Susukan, who gave up to authorities two weeks ago after being wounded in battle.

Susukan has been blamed for kidnappings and beheadings of hostages, including foreign tourists, and surrenders through a Muslim rebel chief, which has signed a peace deal and was cooperating with the government. He is now in police custody and faces multiple murder charges.