(A street in Peshawar’s old city, 22 March 2010/Janki)

Pakistan’s volatile northwestern city of Peshawar is the largest reservoir of endemic polio viruses in the world, the World Health Organization said on Friday, amid concerns over continuing violence against polio vaccination teams.

Pakistan is also the only polio-endemic country in the world where polio cases rose from 2012 to 2013, the statement said. There were 91 cases last year but only 58 the year before.

Polio can permanently paralyze or kill victims within hours of infection. Intensive vaccination campaigns have almost eradicated the disease worldwide, but it remains endemic in Pakistan, Afghanistan and Nigeria.

In Pakistan, Taliban commanders have forbidden vaccination teams access in some areas. A handful of religious leaders have also denounced the campaign as a plot to sterilize Muslim children.

The rhetoric has fueled violence against the vaccination teams. Many teams travel only with police protection. Last year there were more than 30 attacks on polio teams.