A woman has claimed the remains of one of two suspects behind an explosion last week that killed three soldiers and three civilians, saying the man was her Filipino son.

That brought investigators a step closer to concluding that the bombing was the first case of local militants carrying out a suicide attack.

Major-General Cirilito Sobejanam, head of the Western Mindanao Command, told reporters yesterday a woman on Monday identified one of the suspects as 23-year-old Norman Lasuca.

The last time she saw him was about four years ago, she said.

She added that she and her son belonged to a Muslim ethnic group known as the "Tausug", and that her husband was a Muslim convert.

At a separate news briefing yesterday, Brigadier-General Edgard Arevalo said that samples were taken from the woman and the suspect for DNA testing.

"If it's positive, then we can say conclusively that the person is Filipino, and that the person is the son of the claimant," he said.

General Oscar Albayalde, head of the 170,000-strong police force, said on Monday that Filipinos were behind last Friday's attack on the camp of the 1,500-strong 1st Brigade Combat team, which was specially trained to go after militants linked to the Islamic State in Iraq and Syria (ISIS).

"What we know, and the (military) knows this, (is that) they are Filipinos. They are not foreign nationals," he said.

However, Defence Secretary Delfin Lorenzana said in a separate news briefing that nothing was conclusive yet. "Somebody said the bombers were Indonesians, somebody said Filipinos, but let us wait."

If confirmed, the information suggests that ISIS' ultra-radical teachings have taken deeper roots among Filipino militants.

"Yes, yes, I believe… this has raised the level of extremism here," said Mr Lorenzana.

In the attack last Friday, two militants set off bombs strapped to their bodies at the temporary camp of the 1st Brigade Combat team in Indanan town on Jolo island, in the Philippines' restive south.

Three soldiers who were manning the camp's gate were killed, along with three civilians who were nearby. The two attackers were also killed. ISIS has claimed responsibility for the attack.

A tweet last Saturday by the director of the Site Intelligence Group, which monitors extremist groups, showed a photo of two militants whom ISIS said carried out the attack. They appear to be in their twenties, are Asians and wearing vests laden with bombs.

There have been two other instances of suicide bombings in the Philippines, but these involved foreign militants.

Security officials and some analysts have long assumed that local extremist groups such as the Abu Sayyaf, although pledging allegiance to ISIS, eschew suicide attacks as a weapon.

The Abu Sayyaf, founded in the 1990s with seed money from Osama bin Laden's Al-Qaeda network, has been tagged as the top suspect in the attack.

"I think we have a lot of work to do," Mr Lorenzana said yesterday.

On Monday, security forces arrested a Kenyan believed to be part of Al-Qaeda's East Africa wing, Al Shabaab, in Zambales province, north of Manila.

Cholo Abdi Abdullah had been studying to be a pilot, and was plotting to hijack a plane, police said.