More than 7.5 million children under five would receive anti-polio vaccines in 21 out of Afghanistan's 34 provinces, a statement of the country's Ministry of Public Health said.

Unidentified assailants opened fire on a vehicle in Khyber Pakhtunkhwa region of Pakistan which left at least one polio programme official dead, media reports said.

At least two policemen, who were escorting a polio vaccination team, died when armed men opened fire on them in Pakistan's Quetta region on Tuesday.

Taliban security officials have arrested four people accused of killing four polio vaccinators and two Taliban affiliates in Kunduz province of Afghanistan.