MANILA - A third victim has died in an explosion in Isulan, Sultan Kudarat earlier this week, police said Thursday.

The victim, identified as Wel Mark John Lapidez, fell into a coma due to shrapnel wounds on his head before succumbing to his injuries at the hospital, said Isulan police chief Supt. Celestino Daniel Jr.

A young girl and another festival goer were also killed in Tuesday's blast.

A man left the improvised bomb in a bag near a grocery store as crowds gathered to celebrate the town's founding anniversary but he and an accomplice escaped, the military had said.

The Islamic State claimed the attack, which comes less than a month after a van bomb ripped through a military checkpoint on the neighboring island of Basilan on July 31, killing 10 people.

• Preacher arrested over Basilan van blast

It was "highly likely" that the pro-IS Bangsamoro Islamic Freedom Fighters (BIFF) plotted the attack, said Brigadier General Cirilito Sobejana.

A military spokesman said the blast could have been in retaliation for offensives against the BIFF, adding the group had planned bomb attacks in parts of the southern region of Mindanao.

"They want to create and sow terror in the area," regional military spokesman Captain Arvin Encinas told AFP, adding two soldiers were among the wounded.

• Military links BIFF to Sultan Kudarat blast

The IS also claimed responsibility for the Basilan van bombing.

President Rodrigo Duterte put Mindanao under martial rule until the end of this year after pro-IS militants seized the southern city of Marawi last year.

On Wednesday, Duterte's aides condemned the bombing saying it could prompt the president to extend martial law in the area.

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• Sara Duterte open to possible extension of martial law in Mindanao

The recent blasts follow the Duterte government enacting a law to create greater autonomy for the Muslim minority in the south and which is hoped will help end the conflict.

• Duterte open to modifying Bangsamoro law

The mother of the girl who died in Tuesday's bombing pleaded with authorities for justice.

"I hope they help us and catch the perpetrators," Nezel Alayon said in between tears.

The local government on Wednesday offered P1 million for information that could lead to the arrest of the bomber.

The situation around the blast site has returned to normal as roads and business establishments re-opened, said Sobejana.

The decades-long insurgency in Mindanao has left more than 100,000 people dead by government count.

With reports from Agence France-Presse; Zhander Cayabyab, DZMM