MANILA, Philippines — Security forces are searching for four people suspected to be behind last week’s powerful blast that killed 14 people and injured 67 at a busy night market in the southern Philippine city of Davao, police said Monday.

Police have artist sketches of a man who left a backpack containing the powerful improvised bomb before it exploded on Friday, said the national police chief, Ronald dela Rosa, adding that composite sketches were being prepared for the others — two women and a man.

Abu Sayyaf Muslim militants claimed responsibility for the blast, but dela Rosa said officials were not discounting the possibility that it could be the handiwork of drug traffickers or drug lords in collusion with the militants.

According to witnesses, the man who left the backpack at the open-air market hurriedly walked away from the scene, pretending not to hear those calling his attention, said the regional police chief, Chief Superintendent Manuel R. Gaerlan. A few seconds later, the bomb went off, he said.

Davao Mayor Sara Duterte has offered a 2 million peso ($42,900) reward for the perpetrators’ arrest. She said the heads of the police and military in the city would be replaced for failing to avert the bombing.

Philippine President Rodrigo Duterte declared a nationwide “state of lawlessness” Saturday after the blast in his hometown, where he was the longtime mayor. The current mayor is his daughter.

The president said his declaration did not amount to an imposition of martial law. It allows troops to be deployed in urban centers to back up the police in setting up checkpoints and increasing patrols, he said.

Duterte was to leave Monday afternoon for a summit of Asian leaders in Laos, where he is also expected to meet with President Barack Obama.