ISLAMABAD — Two gunmen on motorcycle shot and killed a polio vaccinator in the southwestern Pakistani city of Chaman on Thursday, bringing the death toll among vaccinators working in the country’s anti-polio drive to at least three this week, officials said.

The shooters opened fire on a group of vaccinators when they were at the front gate of a house in the remote village of Sultan Zai, near the border with Afghanistan, said Samiullah Agha, who is the assistant commissioner of Chaman.

Two members of the vaccination team were hit: Nasreen Bibi, 35, was killed, and Rashida Afzal, 24, was critically wounded, Mr. Agha said in an interview. Vaccination was suspended for an indeterminate period of time in the Chaman area after the shooting.

“The gunmen fled after the attack,” Mr. Agha added. “Security forces have launched a search operation in the area.”