At least 15 people were killed on Wednesday when a suicide bomber targeted a polio eradication center in Pakistan's western city of Quetta, the latest militant attack on the anti-polio campaign in the country.
The Pakistani Taliban and its splinter group Jundullah, which has pledged allegiance to Islamic State, both claimed responsibility for the attack.
Most of the dead were police who had arrived in a van to escort the center's staff on their vaccination rounds in the underdeveloped western province of Balochistan. One civilian was killed, and at least 25 people were injured.
A surviving police constable, Iqrar ul Hussain, told VICE News the attack took place around 10am. "Our force was ready to move out with the polio vaccination team, then a blast took place. For a few seconds I couldn't see anything because of the dust. When I was able to see, there were dead and injured bodies of my colleagues on the roadside."
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 told Reuters by telephone.
Polio workers have been targeted by Islamist militants for years, who have accused all vaccination programs of being a front for Western spy agencies since 2011 CIA plot set up a fake hepatitis-C vaccination campaign in Pakistan in an attempt to locate Osama bin Laden.
Rumors have also been spread that the vaccines secretly sterilize Pakistani children, or contain pig fat or alcohol.
Many Pakistani parents now refuse to get their children vaccinated, leading to a spike in polio cases in Pakistan. Dozens of vaccination workers have been killed.
Pakistan and neighboring 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.
_Mohammad Zubair Khan and Reuters contributed to this report. _