MANILA — A former mayor accused of being a drug trafficker in the Philippines was killed Thursday after he attempted to grab a gun from officers while being transported to detention in the capital, Manila, the police said.

Montasser Sabal, the former mayor of the southern town of Talitay, was arrested late Wednesday with three of his companions as they prepared to depart from the port of Batangas, south of Manila. Mr. Sabal’s brother, Abdul Wahab Sabal, who was also a mayor, was shot and killed outside a Manila hotel last year.

Both men were among 44 mayors, vice mayors and other officials identified by President Rodrigo Duterte in May 2019 as being “narco politicians.” More than half of those on the list have already been killed by the police under similar circumstances in which the authorities said the suspects resisted arrest and attempted to grab officers’ firearms.

The police said Mr. Sabal had “grabbed the service firearms of the police escort” while he was being transported.

Gen. Guillermo Eleazar, the national police chief, said Mr. Sabal was a “high-value target” who was a former police commando trained in bomb disposal. Apart from drug trafficking, General Eleazar said Mr. Sabal was suspected of providing the material used in a 2016 bombing that killed 14 people at a night market in Davao City, Mr. Duterte’s hometown.

It was not clear why Mr. Sabal was not restrained while he was being transported to detention. A full investigation is underway, General Eleazar said.

Mr. Sabal’s death came three days after the International Criminal Court’s departing chief prosecutor, Fatou Bensouda, asked the court to open a full investigation into Mr. Duterte’s bloody war on drugs, which began after he took office in June 2016.

Ms. Bensouda’s office had been investigating the drug war until March 2019, when Mr. Duterte’s government pulled out of the international treaty that established the court. But Mr. Duterte’s decision to leave the treaty would not stop the court from conducting a full investigation into crimes committed during the years his country was a signatory.

“Following a thorough preliminary investigation process, the available information indicates that members of the Philippine National Police and others acting in concert with them have unlawfully killed between several thousand and tens of thousands of civilians” in the brutal antidrug campaign, Ms. Bensouda said in a statement on Monday.

She said there was reason to believe that some of those who carried out the killings were either themselves police officers or “private citizens recruited, coordinated, and paid by police to kill civilians.”

In her request, Ms. Bensouda wrote that the total number of civilians killed in the drug war from July 2016 to March 2019 “appears to be between 12,000 and 30,000.” The Philippine government claims the number is roughly 8,000.

“Police and other government officials planned, ordered, and sometimes directly perpetrated extrajudicial killings. They paid police officers and vigilantes bounties for extrajudicial killings,” the request said. The killings were encouraged by officials “at the highest levels of government.”

Reacting to Ms. Bensouda’s request to the court, Mr. Duterte’s spokesman, Harry Roque, said that the president “will never, ever cooperate” with the court investigation, calling it “politically motivated.” Mr. Roque said that anyone slain “in a lawful operation” as part of the country’s war on drugs could be considered “collateral damage” because police officers have a right to defend themselves in the line of duty.