Van-riding assailants gunned down the vice mayor of a small Philippine city south of Manila on Saturday, police said, the third such brazen killing of a local official in the past week.

Vice Mayor Alexander Lubigan of Trece Martires city and his driver were riding in a pickup van when they were shot and killed in front of a hospital in his city in Cavite province, according to a police report. The gunmen escaped.

A special team of investigators was formed to try to identify the killers and establish the motive for the attack in one of the bloodiest weeks for local officials. The series of killings has renewed calls for more effective gun control in a country long plagued by a surfeit of unlicensed firearms.

On Monday, Mayor Antonio Halili was shot in the heart and killed while singing the national anthem in a flag-raising ceremony in his city of Tanauan, south of the capital. The next day, Mayor Ferdinand Bote of northern General Tinio town was shot and killed in an SUV by motorcycle-riding assassins. The killers of both mayors remain at large.

Video taken by witnesses of the moments when Halili and Bote were killed have been widely viewed online and renewed fears of unabated lawlessness.

The back-to-back killings prompted an opposition senator to call the Philippines — where more than 4,000 mostly impoverished drug suspects have been killed under President Rodrigo Duterte's anti-drug crackdown — the "murder capital of Asia."

At least nine mayors have been killed under Duterte, who took office in June 2016, including four who have been linked by Duterte and authorities to illegal drugs. Halili had been included on a government list of suspected drug personalities, but he had vehemently denied any involvement.

An association of local officials has asked Duterte's administration to be allowed to vet the government's list of drug-linked officials and to be notified when suspects are added or removed from the list. Human rights watchdogs regard it as a "hit list," a charge denied by law enforcers.