At least 10 people were killed and dozens wounded -- including soldiers and police -- in a twin bombing Monday involving a suicide attacker on a southern Philippine island that is a stronghold of Islamist militants, officials said.

The attack happened in Jolo in Muslim-majority Sulu, where government-backed security forces have long been fighting the Abu Sayyaf group.

Five soldiers and four civilians were killed in the first blast, when an improvised explosive device attached to a motorcycle parked outside a supermarket blew up, Lieutenant General Corleto Vinluan told reporters.

Sixteen soldiers were wounded in the explosion, which happened at around midday.  Around 20 civilians were also hurt, Lieutenant Colonel Ronaldo Mateo said, citing the local mayor.

A soldier saw a person leave the motorbike outside the grocery store "where there were a lot of people" including members of the military. It immediately detonated, Mateo said. "Our soldiers are conducting security operations. That was the time that the improvised explosive device detonated," he said.

There was a second blast a short time later in the same street when a female suicide attacker blew herself up as police cordoned off the area, killing one person and wounding around six officers, Vinluan said.

A solider had been trying to apprehend the bomber when she detonated her explosives, he added.  Abu Sayyaf was "most probably" behind the double bombing, Mateo said.

Blasts follow arrest 

Listed by the United States as a terrorist organisation, Abu Sayyaf is a loose network of Islamic militants blamed for the Philippines' worst terror attacks as well as kidnappings of foreign tourists and Christian missionaries.

They also have ties to Islamic State militants seeking to set up a caliphate in Southeast Asia. Monday's explosions come after the arrest earlier this month of an Abu Sayyaf leader on the southern island of Mindanao. 

Security forces had been on alert for possible reprisal attacks after detaining Abduljihad Susukan, who is accused of kidnapping and beheading several foreigners. He has been charged with 23 murders, five kidnappings and six attempted murders, police have said.

President Rodrigo Duterte's spokesman Harry Roque condemned the "dastardly attacks" and issued condolences to the families and loved ones of those killed. "We call on the residents of Jolo to stay vigilant and report suspicious personalities and unattended items in their areas," Roque said.

The Philippine Coast Guard issued a "red alert" for Sulu and several other areas in the restive south as it assists the military and police in responding to the incident. 

The explosions happened near a Catholic cathedral in Jolo where two suicide bombers blew themselves up in January 2019 killing 21 people. It was blamed on a group linked to Abu Sayyaf.