Unidentified militants opened fire on a polio vaccination team in Pakistan on Tuesday, killing one of those handing out doses and two policemen, while a child was injured, officials said, but there was no immediate claim of responsibility.
The attack in the northwest region bordering Afghanistan comes a day after Pakistan launched its latest national campaign to stamp out the virus, which still poses a health threat in the South Asian nation, although mostly eradicated elsewhere, reports Reuters.
"Unknown militants opened fire at a polio team," according to an official report from the region's deputy commissioner that listed the casualties and added that a search for the culprits had begun.
Pakistan reported three new polio cases this year after a gap of 15 months, all in the northwest province of Khyber Pakhtunkhwa that borders Afghanistan.
Insecurity and misinformation are widespread in the region and offer challenges to authorities trying to reach every child who needs the polio vaccine, Bill Gates, a key funder of charitable eradication campaigns, wrote on his blog in May.
At least one Islamist militant group in the region has previously claimed similar attacks on polio teams, falsely portraying the campaigns as a Western conspiracy to sterilise children.
In March, a woman who administered polio vaccine doses was killed in same region as she returned home from work.
Pakistan's polio campaign, the latest of several, is targeting its 25 districts most vulnerable to the disease, Prime Minister Shehbaz Sharif has said.
"Let us make it a success and defeat polio, once and for all," Sharif said in a Twitter message at the outset of this week's campaign while expressing regret the highly infectious disease had not yet been eliminated.
Pakistan and Afghanistan are the only two countries in the world still struggling to eradicate polio.