At least 14 people were killed Wednesday when a bomb tore through a polio vaccination center in southwestern Pakistan.

The New York Times reported that 13 of the dead were police officers at the site in Quetta. Authorities said 23 people were wounded. Area doctors told reporters that five of the wounded are in critical condition.

The police officers guard the health workers at the clinic. The health staff are often targeted by Islamist militants in Pakistan, according to the New York Times.

A spokesperson for the Pakistani Taliban claimed responsibility for the suicide bombing in a statement to reporters. The Pakistani Taliban is an extremist alliance of militant organizations. They are waging an insurgency against the state of Pakistan. The alliance is responsible for killing thousands of Pakistanis in recent years.

A senior Pakistani police officer told reporters that the suicide bomber had at least seven kilograms of explosives strapped to his body. The bomber walked into a group of security forces and health workers, and detonated the device.

The incident happened during a three-day immunization campaign to eliminate polio from Pakistan.

Such immunization campaigns meet resistance. Religious groups see the anti-polio campaign as a Western conspiracy to sterilize Muslims. Islamist militants suspect that the health centers are homes for espionage.

At least 80 people have been killed in related immunization center attacks since 2012.

Despite the attacks, 2015 saw a big drop in polio cases in Pakistan. Health officials said the country saw an 84 percent decline in polio cases last year.

I'm Kathleen Struck.

Ayaz Gul wrote this story for VOAnews. Jim Dresbach adapted it for Learning English. Kathleen Struck was the editor.