Manila: The Philippine police said on Friday that they had arrested two additional suspects in the September bombing of a night market that killed 15 people in the hometown of President Rodrigo Duterte, officials said, blaming a small militant group for the attack.

The Criminal Investigation and Detection Group said the two were arrested on Tuesday in Davao City, the site of the attack, where Duterte used to be mayor.

The police identified the suspects as Zack Haron Velasco Lopez and Jessy Vincent Quinto Original, saying they had outstanding arrest warrants alleging terrorism.

Duterte had declared a state of emergency across the southern Philippines, which includes Davao City, that gives the armed forces police powers to aid in the manhunt.

At least seven people had previously been arrested in the bombing, with the police saying that they belonged to the Maute group, a small band of militants based in the south that has been trying to attract the attention of Daesh (the self-proclaimed Islamic State of Iraq and Levant) in the Middle East.

An attempted bombing outside the US Embassy in late November has also been attributed to the group. Military and police officials said that the assault was an effort to divert attention from a government offensive in the south that Duterte had ordered.

That offensive dislodged the Maute group in the southern province of Lanao del Sur, where members had briefly taken over government buildings and flew a black flag bearing the insignia of Daesh.

After a week of intense fighting, the military dislodged the Maute group, killing 61 members. But dozens more were believed to have escaped.

Duterte visited the area afterward and warned that the military would crush the group. He has also linked the militants directly to Daesh, though the military has offered little evidence of actual ties between the organisations.

Rommel Banlaoi, who oversees the Philippine Institute for Peace, Violence and Terrorism Research, said the Maute group was once associated with Muslim rebels who have signed a peace deal with government. They are believed to number in the dozens and operate under a loose command structure.

“They may be small, but are capable of causing terror in a big scale,” he said, adding that the group has been training militants to carry out more bombings in the south.

The group was an emerging security threat, he said, and could rival Abu Sayyaf, another militant organisation that is still holding several local and foreign hostages. That group has been blamed for some of the country’s worst terrorist attacks, including a ferry bombing that killed more than 100 people in 2004.