Islamabad, Aug 17 (IANS): Unidentified gunmen shot and killed two police officers in Pakistan deployed to guard medics administering the polio vaccine.

The incident took place on Tuesday in Khyber Pakhtunkhwa's Tank district during a door-to-door vaccination drive, dpa news agency quoted a local police official as saying.

He said the gunmen, who were riding a motorcycle, had fled the scene.

No group has claimed responsibility for the attack.

On Monday, the provincial government launched the vaccination drive to jab more than a million children up to the age of five.

Pakistan had a polio-free run for almost a year but 14 new cases, all from the violence-stricken province, have been reported in the past few months.

Pakistan is one of the few countries in the world where new polio cases still surface, though the number of affected children has declined massively compared to 306 in 2014.

Neighbouring Afghanistan also has a similar problem, with the UK and US both recently recording polio in waste water.

Militants linked to Al Qaeda often attack health workers in Pakistan.

Dozens of vaccine handlers and security officials have been killed by militants in the past.

They accuse the health workers of acting as spies and claim the polio vaccine is intended to make Muslim children sterile.