Islamabad(CNN) A blast near a polio vaccination center in Pakistan killed 14 people and injured more than a dozen more, officials said -- an attack later claimed by two Islamist militant groups.
Among the dead in Wednesday's attack in the city of Quetta were 13 policemen and a paramilitary trooper, said Balochistan province Home Minister Mir Sarfaraz Bugti.
The blast is under investigation, he said.
Militants have targeted anti-polio campaigns in Pakistan for decades in an effort to beat back government influence, CNN's Nic Robertson said.
In 2011, U.S. intelligence officials used a vaccination program to help in their hunt for Osama bin Laden. Under cover of the program, the CIA sought to collect DNA samples from relatives of the al Qaeda leader to verify his presence in a compound in Abbottabad, Pakistan.
The revelation of the CIA scheme reinforced the militants' existing fear of vaccinations.
Two groups made apparently competing claims of responsibility for Wednesday's attack.
The Pakistan Taliban, known as the Tehreek-e-Taliban Pakistan, or TTP, said it was behind the attack. But so did the TTP splinter group Jundallah.
Jundallah spokesman Ahmad Marwat told CNN via text that this group was responsible and that it "will always target polio teams."
The lack of trust and fears of attacks on vaccination centers have led many Pakistani parents to refuse mandatory vaccinations. Last year, the government arrested at least 500 parents for refusing to vaccinate.
Vaccines are credited with wiping out polio in most parts of the world. But Pakistan is an exception, the Global Polio Eradication Initiative says. The South Asian nation has led all others in new polio cases in recent years.