COTABATO CITY (3rd UPDATE) - Fifteen people, including a policeman, were hurt when a grenade exploded outside a church in North Cotabato, Mindanao on Saturday, police said.

The blast occurred some 50 meters from the Santo Niño Church in the town of Midsayap, while a Christmas Eve mass was being held.

Four of the victims were brought to Pesante Hospital; eight were brought to Amado District Hospital; and one victim was rushed to the Cotabato Regional Medical Center.

The Philippine National Police and the Armed Forces of the Philippines identified the victims as Dagul Celes, Cheyserr Mae Rosete, Arnel silvano, Jenelyn Silvano, Regor Pedrosa, Jofer Asis, Leah Butan, Joy Singco, Kent Steven Paquito, Jazza Mae Banlawi, SPO4 Johny Caballero, Jonel Orquiza, Kent Pacquiao, Russel Jarapan and Clint Silvano.

Three of the victims sustained serious injuries.

The grenade exploded under a patrol car of the Midsayap Police. Two vehicles owned by private individuals were also heavily damaged in the incident.

No group has claimed responsibility for the Mindanao attack, but Muslim rebels and Islamist extremists are known to be active in the province, where there have been blasts in the past.

Bernardo Tayong, Midsayap town police chief, said most of the injured had been standing outside the Santo Niño parish church.

Father Jay Virador said the blast sent the congregation fleeing.

"There was no more concluding prayers as there was a commotion," Virador said. "People hurriedly left the Church."

Tayong said bomb experts were still at the site. There were reports that another grenade or improvised bomb was also left in the area.

"Our details are sketchy yet," he said.

The US embassy in Manila said citizens had warned against travelling to the volatile southern islands due to kidnapping and bombing threats.

In September, 14 people died and 70 were wounded when an improvised bomb exploded in a crowded market in Davao City, the hometown of President Rodrigo Duterte.

Nine people, who were linked to an Islamic State militant-affiliated group, have been arrested for the attack. -- With Reuters