The World Health Organization on Friday declared Pakistan's troubled northwestern city of Peshawar as the world's "largest reservoir" of polio and called for urgent action to boost vaccination.
Almost every polio case in 2013 in Pakistan, one of only three countries where the crippling disease remains endemic, could be linked genetically to strains of the virus circulating in Peshawar, said the WHO.
Khyber Pakhtunkhwa province, of which Peshawar is the capital, and adjoining tribal districts where Taliban and Al-Qaeda linked militants have hideouts are particular polio hotspots.
Efforts to stamp out the disease have been hampered by opposition from militant groups, who see vaccination campaigns as cover for espionage, as well as long-running rumours about the drops causing infertility.
"With more than 90 percent of the current polio cases in the country genetically linked to Peshawar, the (city) is now the largest reservoir of endemic poliovirus in the world," the WHO said in a statement.
Polio is also endemic in Afghanistan and Nigeria, but of the three countries only Pakistan saw a rise in cases from 2012 to 2013, said the global health body.
Tests have found that 83 out of the 91 polio cases in Pakistan last year were genetically linked to strains in Peshawar, while 12 out of 13 cases reported in Afghanistan were also linked.