A polio vaccination worker was killed and others are missing in Pakistan. Pictured is a medical worker administering the vaccine to infants in India Jan. 18, 2015. Reuters/Jayanta Dey

Gunmen attacked a vehicle carrying a polio vaccination team in the Khyber Agency in Pakistan. Dawn newspaper reported the driver was killed and a polio volunteer was injured. Security officials said polio workers were on their way to a vaccination session in the Landi Kotal's Lowi Shalman area. Officials cordoned off the area.

The area straddles the Afghanistan border and has seen recent military action, the New York Times reported. Polio vaccination workers are frequently targeted by Taliban militants who accuse medical workers of being Western spies.

Earlier, Pakistan Today reported two medical workers and their police escort disappeared in a remote area of Baluchistan as they handed out polio vaccines, authorities said. Nazir Ahmed Khetram, the deputy commissioner in the Zhob district, told a private media outlet the workers were last seen about 11 p.m. Friday.

“It is a remote area. There is no proper communication system. Which is why we are facing difficulty in tracing them,” he said.

Pakistan Today reported the medical workers were supposed to provide vaccines in Murgha Gibzai, Toda Ghibzai and Barkwal union councils -- considered "high-risk" areas -- but never arrived at their destination. Zhob said investigators had yet to determine whether they had been kidnapped.

Resistance to polio campaigns in Pakistan have been growing since the 2011 U.S. Navy SEAL raid that killed Osama bin Laden in Abbottabad. The CIA had used a vaccination campaign as a cover for gathering information on the whereabouts of the al Qaeda leader.

Pakistan is one of three countries -- Afghanistan and Nigeria are the other two -- and where polio still runs rampant, and efforts to eradicate the disease in all three have been met by resistance from Muslim fundamentalists who have labeled vaccination campaigns un-Islamic. The campaigns also are hampered by long-running rumors the vaccination causes infertility.

Pakistan reported 305 polio cases in 2014. As recently as 2005, the number of cases was down to 28.