The attack in the region bordering Afghanistan comes two days after Pakistan launched its latest national campaign to stamp out the virus, which still poses a health threat in the South Asian nation, although mostly eradicated elsewhere.

“Unidentified armed men opened fire on polio vaccination team in a subdivision of Bajaur tribal district as they were on the vaccination campaign,” district police officer Waqas Rafique told Reuters.

The Pakistani Taliban, or Tehreek-e-Taliban Pakistan (TTP) said in a statement their fighters had killed a police officer accompanying the polio team and injured one other.

The statement made no mention of the polio worker or the reason for the attack.

Previously Islamist rebel groups in the region have claimed similar attacks on polio teams, falsely portraying the inoculation campaigns as a western conspiracy to sterilise children.

Pakistan began its latest national campaign earlier this week, aiming to administer the vaccine to up to 30 million children, the prime minister’s office said.

Pakistan and Afghanistan are the only two countries in the world still struggling to eradicate polio.

A local police union group called for a strike by policemen and a boycott of security duties for the vaccination campaign in the Bajaur district following the killing of their colleague.