A policeman was killed Tuesday in an attack by two armed men on a team administering polio vaccines in the northwestern town of Mardan, a Pakistani police officer told Efe.

The incident occurred shortly after noon when two unknown men riding a motorcycle opened fire on the officer, who was providing security while two vaccination team members were inside a home in the Ghalla Dar area, Jamshad Khan said.

This attack is part of a series of such strikes against vaccination teams that in less than two months have taken the lives of more than a dozen people around Pakistan.

Two members of a vaccination team died less than a month ago when a bomb exploded as they were passing by in the northwestern Khurram region, and two days earlier a police officer was killed in the nearby Swabi district in circumstances similar to Tuesday's attack.

Although the Taliban have not claimed responsibility for the attacks against the vaccination campaign, groups linked to them based in the volatile tribal areas bordering Afghanistan have threatened to attack health workers.

Pakistan is one of only three countries - the other two are Afghanistan and Nigeria - where polio is still endemic and authorities, working with international agencies, are making a significant effort to immunize all children under age 5 against the disease. EFE