The Roman Catholic Church in the Philippines slammed President Rodrigo Duterte’s war on drugs in a sermon delivered during Sunday’s services, marking its strongest opposition yet to a flagship policy that has led to the deaths of more than 7,000 people in the last seven months.

In a pastoral letter by the Catholic Bishops’ Conference of the Philippines, church leaders called Mr. Duterte’s antinarcotics campaign a “reign of terror in many places of the poor.” They said that while illegal drug trafficking needs to be stopped, “the solution does not lie in the killing of suspected drug users” and dealers.

Opposition to Mr. Duterte’s drug war has intensified in the past week, following the alleged murder in police custody of a South Korean businessman after he was abducted by antinarcotics officers. After strangling the businessman, Jee Ick-joo, to death, the officers allegedly pretended that he was still alive to extract a ransom from his wife.

The incident, which took place in October but came to light last month, shocked the political establishment in the Philippines, leading to calls for police chief Gen. Ronald Dela Rosa, a staunch ally of the president, to step down. Mr. Dela Rosa kept his job, but promptly suspended all antinarcotics operations of the police force, handing the responsibility over to a much smaller drug enforcement agency.

Sunday’s criticism from the Catholic church piles further pressure on the government at a time when it is reeling from Mr. Jee’s murder, and it might influence public opinion. The Philippines is one of the world’s most Catholic countries, with more than 80% of Filipinos identifying as belonging to the religion. Sunday church sermons are an important part of daily life for many millions of people in the country, who turn to their faith for guidance on matters of morality.