The president of the Philippines has declared a nationwide “state of lawlessness” after suspected Islamic extremists detonated a bomb that killed 14 people and wounded about 70 in Davao, his home city.

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

Abu Rami, a spokesman for the Islamist militant group Abu Sayyaf, claimed responsibility for the blast near a night market and an upmarket hotel, but Duterte said investigators were looking at other possible suspects, including drug cartels, which he has targeted in a bloody crackdown.

“These are extraordinary times and I supposed that I’m authorised to allow the security forces of this country to do searches,” Duterte said on a visit to the scene of the attack. “We’re trying to cope up with a crisis now. There is a crisis in this country involving drugs, extrajudicial killings and there seems to be an environment of lawless violence.”

Duterte was mayor of Davao for years before being elected president in June. He has postponed a visit to Brunei due to begin on Sunday.

The bombing in the city of 2 million people, which is almost 1,000km (610 miles) south of Manila, came as Philippines forces were on alert amid an ongoing military offensive against Abu Sayyaf extremists in southern Sulu province. That conflict intensified last week after the militants beheaded a kidnapped villager.

The militants threatened to launch an unspecified attack after the military said 30 of the gunmen were killed in the weeklong offensive.

Rami is the son-in-law of Mohammad Said, an influential militant commander who was killed in the ongoing Sulu offensive. Davao’s deputy mayor, Paulo Duterte, the president’s son, said that militants linked to the Islamic State group had threatened the city.

Some commanders of Abu Sayyaf, which is blacklisted by the United States and the Philippines as a terrorist organisation for deadly bombings, ransom kidnappings and beheadings, have pledged allegiance to Isis. The military, however, says there has been no evidence of a direct collaboration and militant action may have been aimed at bolstering their image after years of setbacks.

The government’s communications secretary, Martin Andanar, said that the bomb appeared to have been made from a mortar round and that doctors reported many of the victims had shrapnel wounds.

Armando Morales, a 50-year-old masseur, said the explosion threw him off his chair. He said he saw at least 10 people lying wounded on the ground – mostly fellow masseurs and their customers.

Ned Price, US National Security Council spokesman, said that authorities in the Philippines continue to investigate the cause of the explosion, and the United States was ready to assist it if necessary.

The US president, Barack Obama, will have an opportunity to offer his personal condolences to Duterte, with the two leaders planning to meet on the sidelines of the summit of the Association of Southeast Asian Nations leaders in Laos next week, Price added.

Communist rebels, who have been waging an armed struggle since 1968, also maintain a presence in rural areas neighbouring Davao.

Duterte became well known for bringing relative peace and order to Davao with hardline security policies, while also brokering local deals with Muslim and communist rebels.

However in 2003, two bomb attacks blamed on Muslim rebels at Davao’s airport and the city’s port within a month of each other killed about 40 people.

Duterte has in recent weeks pursued peace talks with the two main Muslim rebel groups. Its leaders have said they want to broker a lasting peace.

Associated Press in Davao