The World Health Organization has declared Pakistan's restive northwestern city of Peshawar the world's "largest reservoir" of polio.
The international group on Friday called for urgent action to boost vaccination to prevent the crippling disease.
WHO also said almost every polio case in 2013 in Pakistan could be linked genetically to the strains of the virus circulating in Peshawar.
Militants frequently attack polio workers in Peshawar and adjoining tribal districts, accusing them of being Western spies or part of a plot to sterilize Muslims.
Tests found that 83 of the 91 polio cases in Pakistan last year were genetically linked to strains in Peshawar. In neighboring Afghanistan, 12 of 13 polio cases were also linked to Peshawar.
The disease is highly infectious and can cause irreversible paralysis.
Pakistan is one of three countries where polio remains endemic. However, it is the only country that experienced a rise in polio victims last year. Polio is also endemic in Afghanistan and Nigeria.
The Global Eradication Initiative says until poliovirus transmission is interrupted in these countries, all countries remain at risk of importation of polio.