Gunmen on a motorcycle shot and killed a police officer returning home after security duty with polio vaccination workers in Peshawar, police said.

The killing came during one of two attacks in Khyber Pakhtunkhwa on Sunday on police providing security for polio vaccination teams.

The officer was returning home on his motorcycle after providing security for a polio team, said Iftikhar Khan, the area police chief.

Meanwhile, a roadside bomb exploded as a police van passed by while escorting a polio vaccination team in the Ladha area of the South Waziristan tribal district. The blast wounded an officer in the van, said police officer Shaukat Ali.

In both attacks, members of the vaccination teams were unhurt. No one immediately claimed responsibility for either attack.

The violence came two days after the government launched polio vaccination drives in 18 districts of the province to eradicate the crippling disease by the end of the year.

Militants often target polio teams and police assigned to protect them claiming the vaccination campaigns are a Western conspiracy to sterilise children.

Pakistan and Afghanistan are the only two remaining countries in the world where polio is endemic, after Nigeria was last year declared free of the virus.

Aimal Khan, provincial spokesman for the anti-polio programme, said the goal of the five-day drive was to vaccinate 3.7 million children. Nearly 17,000 trained workers were going home-to-home to administer the vaccines, he said. Police and security forces have been assigned to protect the vaccination teams.