Pakistani opposition leader and former cricket hero Imran Khan has been threatened by militants after criticizing attacks on polio vaccination teams, his party said Thursday.

Khan on Wednesday declared polio workers as soldiers of Islam and said those attacking them were not doing any justice to humanity, Islam or Pakistanis.

Pakistan is one of three countries in the world where polio remains endemic and efforts to stamp it out have been badly affected by attacks on health workers inoculating children.

"Mr. Khan received a threat from Ansarul Mujahideen over his remarks over anti-polio campaign," Shireen Mazari, a senior member of Khan's Pakistan Tehreek-e-Insaaf (PTI) party told AFP.

Ansarul Mujahideen is a little-known militant group linked to the Tehreek-e-Taliban Pakistan, the umbrella Taliban faction in Pakistan.

Northwestern Pakistan, particularly the lawless tribal regions along the Afghan border, is a hotspot for the highly infectious crippling disease.

Last year the Pakistani Taliban banned polio vaccinations in the tribal region of Waziristan, alleging the campaign was a cover for espionage.

Eradication efforts have also suffered due to long-standing rumors that the vaccine was part of a Western plot to sterilize Muslims.

PTI leads the government in the northwestern province of Khyber Pakhtunkhwa and on Wednesday, Khan pledged to spearhead a fresh anti-polio drive, kicking it off by administering drops to children at a hospital himself.

"Those attacking polio workers and policemen deputed to protect them, are not doing any justice to humanity, Islam and people of Khyber Pakhtunkhwa and Pakistan," Khan said on Wednesday.

"Polio workers are mujahid (soldiers of Islam) and we stand by them."

Up to 2.3 million children in nine districts will be targeted in the immunization drive, local officials have said, after 62 polio cases were reported from tribal areas and Khyber Pakhtunkhwa this year.