A POLICE officer assigned to protect polio vaccination workers in north-west Pakistan was killed today and four others were wounded in a suspected militant attack.

Two attackers were killed when police returned fire during the incident in Hangu, a district in Khyber Pakhtunkhwa province bordering Afghanistan, shortly after Pakistan launched its second nationwide anti-polio campaign of the year.

No group immediately claimed responsibility, but suspicion falls on the Pakistani Taliban, which often carries out similar attacks. 

Pakistan and neighbouring Afghanistan remain the only countries where polio has not been eradicated, according to the World Health Organisation.

The weeklong drive aims to reach more than 45 million children under five.

Health workers and the police assigned to protect them are often targeted by militants who claim the vaccination campaigns are a Western conspiracy to sterilise children.

More than 200 polio workers and the police assigned to guard them have been killed in Pakistan since the 1990s, according to officials.