Pakistani authorities said that gunmen attacked a polio vaccination team, killing one health worker and two policemen in North Waziristan.
Gunmen have attacked a polio vaccination team in northwest Pakistan, killing a health worker and two policemen -- the latest deaths in a dangerous campaign to eradicate the disease
"Gunmen came on a motorcycle and opened fire on the vaccination team," senior police offer Ashfaq Anwar said on Tuesday, adding that a child was also wounded by stray bullets.
"The victims died at the scene and the gunmen escaped."
The attack happened in North Waziristan, a region that borders Afghanistan and which was once a significant refuge for Afghan and Pakistan Taliban militants.
Shahid Ali Khan, a senior government official in the district, confirmed the incident.
Pakistan is one of two countries, alongside neighbouring Afghanistan, where polio remains endemic, but where vaccination teams have been targeted by militants.
Opposition to inoculation
Scores of polio workers and security officials guarding them have been killed in militant attacks since 2012.
Opposition to all forms of inoculation in the region grew after the CIA organised a fake vaccination drive to help track down Al Qaeda's former leader Osama Bin Laden in the Pakistani city of Abbottabad.
Pakistan launched its latest vaccination drive on Monday, aiming to inoculate more than 12.6 million children.
In April, Pakistan reported the first case of the debilitating neurodegenerative disease in 15 months.
Since then, 11 polio cases have been reported -- all from the same district where many villagers are against the vaccines.