A suicide bomber killed at least 15 people, most of them police, outside a polio eradication centre in Pakistan's western city of Quetta on Wednesday, the latest militant attack on the anti-polio campaign in the country.
Militant group Jundullah, which has links with the Pakistani Taliban and has pledged allegiance to Islamic State, claimed responsibility for the attack.
The bomb ripped through a police van that had just arrived at the centre to provide an escort for vaccination workers engaged in a drive to immunise all children under five years old in the underdeveloped western province of Balochistan.
"It was a suicide blast, we have gathered evidence from the scene," Ahsan Mehboob, the provincial police chief told Reuters.
"The police team had arrived to escort teams for the polio campaign."
Ahmed Marwat, who identified himself as a commander and spokesman for Jundullah, said the group was responsible. "We claim the bomb blast on polio office. In the coming days we will make more attacks on polio vaccination offices and polio workers," he said by telephone.
Teams in Pakistan working to immunise children against the virus are often targeted by Taliban and other militant groups, who say the campaign is a cover for Western spies, or accuse workers of distributing vaccines designed to sterilise children.
The latest attack killed at least 12 policemen, one paramilitary officer and two civilians, and wounded 25 others, officials said. They estimated the bomb contained about five kilograms (11 lb) of explosives.
Pakistan and neighbouring Afghanistan are the only two countries in the world where polio remains endemic, the World Health Organization says.
The campaign to eradicate the virus in Pakistan has had some recent success, with new cases down last year, but violence against vaccination workers has slowed the effort.
