Three more health workers were killed Wednesday in Pakistan when unidentified gunmen attacked a polio vaccine administration camp, in a fresh wave of violence against the U.N.-backed vaccination drive, taking the total death toll to eight. The U.N. said it is cancelling a three-day vaccination drive following the attacks.  

Gunmen opened fire at the polio vaccination teams in Peshawar, Nowshera and Charsadda, when the health workers were giving polio drops to the children.

A female health worker and her driver died when gunmen in motorbikes sprayed bullets on a car they were travelling in Charsadda, near Peshawar, in the Khyber Pakhtunkhwa region of northwest Pakistan police official Wajid Khan told AFP. 

A health worker was seriously injured by gun shots in a separate incident in Peshawar, and succumbed to his injuries, while health workers escaped unharmed in similar incidents reported from Nowshera.

Police authorities confirmed the firing and said they are investigating into the incident. So far no group, including Taliban, has claimed responsibility for the attacks.

Five female health officials were killed in past two days in the Sindh and the Khyber Pakhtunkhwa region in northwest Pakistan, in attacks against a three-day nationwide polio eradication drive.

The Sindh government had suspended the vaccination drive in Karachi region following the attacks, but the Khyber Pakhtunkhwa government had chosen to go ahead with the campaign Tuesday.

"You know halting the campaign at this stage would create more problems as it's not a one-day phenomenon. If we stopped the campaign it would encourage the forces opposing the polio vaccination," local official Javed Marwat told Reuters.

Pakistan is one of the three countries in the world, which still has the polio endemic, other two being Afghanistan and Nigeria. The government had announced a three-day massive U.N. backed polio vaccination drive to contain the disease, which is being viewed with suspicion by the Pakistanis.

Pakistanis believe that the vaccination drives are part of a western conspiracy to sterilize the Muslims or gather intelligence information.

Taliban have banned the polio vaccination program in the Waziristan region, after the U.S. government used a fake hepatitis vaccination program to confirm the presence of Osama Bin Laden before killing him in an encounter at an Abottabad compound in 2011.         

Pakistani government Wednesday reiterated their commitment to take forward the vaccination drive.

"We cannot and would not allow polio to wreak havoc on the lives of our children," Pakistan Prime Minister Raja Pervez Ashraf said in a statement.