A pressure cooker bomb hit a police van protecting a polio vaccination team in Peshawar Monday, killing two people in the latest in a string of attacks affecting the immunisation campaign.
The attack took place on the third and last day of a UN-backed vaccination campaign in a suburb of the city of Peshawar, police said, adding that a policeman was among the two dead.
Pakistan is one of only three countries in the world where polio is still endemic, but efforts to stamp out the crippling disease have been hit by repeated attacks on health teams.
Militant groups in the restive country have rejected vaccination as a Western plot against Muslims and banned teams from giving out polio drops in some areas.
"It was an IED blast and the target was policemen," Najeebur Rehman, a senior police official told AFP, adding that the bomb went off just as officers reached the village to provide security to polio teams.
Nasir Durrani, police chief for northwestern Khyber Pakhtunkhwa province, of which Peshawar is the capital, confirmed the incident and death toll and said most of the 12 wounded were policemen.
Abdul Haq, a senior bomb disposal expert, said the bomb was made from a pressure cooker, with metal and nails added as shrapnel.
Authorities said a second device was defused close to the site of the first blast and they had halted polio vaccination in Badaber village, where the incident took place.
"A second bomb with five kilograms of explosives has been defused. We have suspended the campaign for time being," Zahurul Islam, a senior government official in Peshawar told AFP.
Islam said the outer wall of the government-run clinic collapsed due to the intensity of the explosion.
Islam said all those wounded in the blast were policemen, adding that a total of 54 polio workers including 24 women were present inside the clinic.
Raheel Shah, another police official, told AFP that polio workers remained safe in the attack, adding that the second person killed in the blast was a volunteer from the village community police.
No one has claimed responsibility for the killing, but last year the Pakistani Taliban banned polio vaccinations in the tribal region of Waziristan, alleging the campaign was a cover for espionage
Polio teams came under attack in Karachi and in the northwest last year, with the killing of nine health workers carrying out vaccinations.