SEOUL (Reuters) – The bodies of three South Koreans with gunshot wounds to the head have been found in the Philippines, a South Korean foreign ministry official said on Thursday, the latest in a string of killings of Koreans in the southeast Asian nation.

Philippine President Rodrigo Duterte has waged a ruthless anti-crime campaign since taking office on June 30 in which more than 3,600 people have died in police operations and alleged vigilante killings.

The bodies of two men and a woman, all older than 40 and all with gunshot wounds to the head, were found on Tuesday in Bacolor outside the capital, Manila, the ministry official said by telephone.

Chief of police at the town of Bacolor, Sonia Alvarez, said the deaths were unlikely to be related to drugs and instead looked like a crime of passion or indebtedness.

A South Korean consular official is working with Philippine authorities on the case, but no motive or suspects have yet been identified, said the official, who declined to be named because he was not authorised to speak to the media.

The Philippine embassy in Seoul declined to comment.

The legs of one of the male victims were bound while the woman’s wrists were tied, the official added.

The case takes to six the tally of South Koreans found dead this year in the Philippines, where more than ten South Korean citizens have been killed each year since 2013, South Korean media said.

(Reporting by Ju-min Park, Additional reporting by Jess Malabanan, Editing by Jack Kim, Clarence Fernandez and Michael Perry)