MANILA (Reuters) - A mayor on Philippine President Rodrigo Duterte’s list of top drugs suspects was killed during a shootout at a prison on Saturday, police said, in the latest high-profile killing in his bloody war on narcotics.

Philippine President Rodrigo Duterte inspects Japan's coast guard drills in Yokohama, Japan October 27, 2016. REUTERS/Kazuhiro Nogi/Pool

Rolando Espinosa, mayor of Albuera town in central Leyte province, turned himself in to the national police chief in August after Duterte asked him and his son, Kerwin, to surrender over their involvement in the drug trade.

Espinosa was later allowed to go home but on Oct. 5 was arrested on charges of illegal possession of drugs and firearms. He is the second local government executive on Duterte’s so-called “narco-list” killed during police operations.

The shootout took place after Espinosa and inmate Raul Yap fired at a team from the Criminal Investigation and Detection Group who was on a mission to serve a search warrant against the detainees for firearms and illegal drugs, police said.

“As a matter of procedure, this incident will undergo investigation to establish the facts and circumstances surrounding the incident,” Eastern Visayas Regional Police Chief Superintendent Elmer Beltejar said.

Some lawmakers expressed alarm over the killing of Espinosa inside his detention cell, with the chairman of the Senate committee on justice and human rights, Senator Richard Gordon, describing it as a “slap in the face” of the country’s criminal justice system.

Gordon said he may file a resolution to look into such drug-related killings, while Senator Panfilo Lacson was quoted by local media as saying that Espinosa’s death was “a clear case of EJK (extrajudicial killing).”

“There’s got to be a lot of questions that must be answered,” Gordon said in an interview with news channel ANC.

Police said they recovered a .45 caliber pistol and a .38 Super pistol from the cells of Yap and Espinosa. A small sachet containing suspected methamphetamine and drug paraphernalia were also found inside Espinosa’s cell, police said.

The presidential palace described Espinosa’s death as “unfortunate” and said an investigation was ongoing.

Espinosa had publicly denied any part in the drug trade but said his son was peddling “shabu” (methamphetamine), which he gets from a jailed Chinese drug trader.

Espinosa’s son, Kerwin, was arrested by Abu Dhabi police last month, according to Philippine National Police chief Director General Ronald dela Rosa.

In October, Samsudin Dimaukom, a powerful mayor in Duterte’s troubled home province of Mindanao, was also killed along with nine of his guards in a shootout, according to police.

More than 2,300 people have been killed in police operations or by suspected vigilantes in connection with the anti-narcotics campaign since Duterte took office on June 30.

Duterte said on Friday his war on drugs had cut back the supply to “very low” levels and thanked China for supporting his crackdown, but swore repeatedly at ally the United States for criticizing it.