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A Pakistani injured polio worker is treated at a local hospital in Peshawar, Pakistan on Wednesday, Dec. 19, 2012. Gunmen shot dead a woman working on U.N.-backed polio vaccination efforts and her driver in northwestern Pakistan, officials said, just a day after similar attacks across the country killed several female polio workers.
PESHAWAR, Pakistan—Pakistani officials say another victim from attacks on U.N. backed anti-polio teams has died, bringing the three-day toll to nine.

Health official Janbaz Afridi says 20-year-old Hilal Khan died on Thursday, a day after he was shot in the head in the northwestern city of Peshawar.

Since Monday, gunmen had launched attacks in across Pakistan on teams vaccinating children against polio. Six women are among the nine anti-polio workers killed in the vaccination campaign jointly conducted with the Pakistani government.

The U.N. has suspended the drive until a government investigation is completed.

Pakistan is one of only three countries where the crippling disease is endemic.

Pakistani polio workers chant slogans during a demonstration against the killing of their colleagues, Wednesday, Dec. 19, 2012 in Islamabad, Pakistan.
Pakistani polio workers chant slogans during a demonstration against the killing of their colleagues, Wednesday, Dec. 19, 2012 in Islamabad, Pakistan. Gunmen shot dead a woman working on U.N.-backed polio vaccination efforts and her driver in northwestern Pakistan, officials said, just a day after similar attacks across the country killed five female polio workers. The placard on right reads, "why is the government silent over the killings of innocent people?" ((AP Photo/Anjum Naveed))

No one has claimed responsibility for the attacks but some Islamic militants accuse health workers of acting as spies for the U.S.

A Pakistani polio worker participates in a demonstration against the killing of her colleagues, Wednesday, Dec. 19, 2012 in Islamabad, Pakistan. Gunmen
A Pakistani polio worker participates in a demonstration against the killing of her colleagues, Wednesday, Dec. 19, 2012 in Islamabad, Pakistan. Gunmen shot dead a woman working on U.N.-backed polio vaccination efforts and her driver in northwestern Pakistan, officials said, just a day after similar attacks across the country killed five female polio workers. ((AP Photo/Anjum Naveed))

A Pakistani polio worker chants slogans during a demonstration against the killing of their colleagues, Wednesday, Dec. 19, 2012 in Islamabad, Pakistan.
A Pakistani polio worker chants slogans during a demonstration against the killing of their colleagues, Wednesday, Dec. 19, 2012 in Islamabad, Pakistan. Gunmen shot dead a woman working on U.N.-backed polio vaccination efforts and her driver in northwestern Pakistan, officials said, just a day after similar attacks across the country killed five female polio workers. ((AP Photo/Anjum Naveed))