MANILA - The Philippine National Police said Monday it raised the second highest alert nationwide after twin explosions at a church in Jolo, Sulu killed 20 and injured some 100 others.

Metro Manila was earlier placed under full alert, the highest in a 3-step scale, according to Director Guillermo Eleazar, chief of the National Capital Region Police Office.

Under the heightened alert, regional police directors were instructed to "initiate further security measures to preempt and prevent similar incidents," the PNP said in a statement.

Checkpoint operations and the implementation of the election gun ban will be also intensified, it added.

Regional police chiefs were given the discretion to raise alert conditions in their areas if necessary, the PNP said.

Aside from boosting checkpoints and patrols in Metro Manila, a full alert means the police will intensify coordination with the military and work leaves of its personnel will be cancelled, Eleazar said.

The Jolo bloodshed came a week after a majority of voters approved the creation of the Bangsamoro, a new region giving Muslims in the south more control over their own affairs.

Sulu, which includes the remote island of Jolo, voted against creating the new region, but the province will still be part of the Bangsamoro because voters from current autonomous region voted in favor of it.

The Islamic State has claimed responsibility for the blasts.

PNP chief Director General Albayalde however said police would analyze bomb fragments seized from the site of the attack to help determine the perpetrators. The explosive was likely detonated using a cellphone, he said.

With reports from Maan Macapagal and Henry Atuelan, ABS-CBN News