Pakistan has launched a new campaign to vaccinate more than 700,000 children in its volatile tribal regions against polio.
The four-day drive in Pakistan's seven tribal agencies -- known as the Federally Administered Tribal Areas -- began on August 25.
Health officials warned that nearly 300,000 children will miss out on the antipolio campaign due to a lack of security in the insurgency-hit region, which borders Afghanistan.
The Pakistani Taliban and other militant groups -- who have strongholds in tribal areas -- oppose the polio immunization campaign, saying it is a cover for U.S. spying.
Some 56 people have been killed in militant attacks on polio teams in Pakistan since December 2012.
Pakistan recorded 91 cases of polio last year.
Pakistan, Afghanistan, and Nigeria are the only countries where polio remains endemic.