MANILA - The Philippine National Police (PNP) on Monday promised an impartial investigation into the alleged gun battle that left Mayor Samsudin Dimaukom of Datu Saudi Ampatuan, Maguindanao and nine of his men dead in North Cotabato.

PNP spokesperson Senior Supt. Dionardo Carlos said policemen involved in Friday's alleged shootout will be punished for any irregularity after a lawmaker and the suspects' relatives claimed that Dimaukom and his bodyguards died in a possible rubout.

"Kung may mali, nakikitang irregularity, mapapanagot nating itong mga pulis na involved sa insidente," Carlos told radio DZMM. [If there is any irregularity, the policemen involved in the incident will be liable.]

Anti-narcotics agents on Friday set up a checkpoint in Makilala, North Cotabato after a "very reliable" source tipped them off that Dimaukom's group will transport illegal drugs, Carlos said, citing initial police reports.

The mayor's convoy, he added, allegedly did not stop at the checkpoint and instead fired at the operatives. They were gravely wounded in the ensuing firefight and were rushed to a hospital but were declared dead on arrival.

Recovered from the group were 13 sachets of shabu and six firearms.

• READ: Maguindanao mayor tagged as 'narco-politician' slain

Maguindanao Rep. Dodong Mangudadatu, however, disputed police account of the shootout, pointing out that the mayor’s car was parked properly and only a few sachets of drugs were confiscated from him.

Solon wants forensic tests on slain Datu Saudi Ampatuan mayor
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Relatives of Dimaukom also noted that most of the men were shot in the head, a supposed indication that they were marked for the kill.

The PNP Internal Affairs will look into these observations and also verify the intelligence information that prompted the operation, Carlos said.

The official also encouraged Mangudadatu and Dimaukom's relatives to air their suspicions before investigators.

"Iyung mga allegation, suspicion po na ganyan, mas maganda pa na ito ay maibigay po bilang observation para mas laong mapagtibay po iyung isinasagawang imbestigasyon kung may pagkakamali po iyung ating mga pulis," he said. [Such allegations, suspicions should be formally submitted as observations to bolster our ongoing investigation on the possible liabilities of the policemen.]

Dimaukom was among 150 officials accused of being drug coddlers by President Duterte in August. The mayor and his wife had turned themselves in to PNP Director General Ronald dela Rosa.

• READ: DUTERTE'S LIST: 'Narco' politicos, lawmen, judges

Dimaukom's death comes days after reports that the PNP has shifted strategy in its blood-soaked drug war to reduce the killing of suspects and put more resources into arresting "high-value targets."

• READ: MAP, CHARTS: The Death Toll of the War on Drugs