An injured man is carried out of an ambulance in Peshawar, northwest Pakistan.
An injured man is carried out of an ambulance in Peshawar, northwest Pakistan. Reuters

At least 11 people have been killed and several more injured in a bomb attack on a polio vaccination team in northwest Pakistan.

A series of roadside bombs exploded as the convoy drove through a village in Khyber Pakhtunkhwa province, near the Afghan border.

Paramilitary troops guarding the anti-polio campaigners were killed in the attack, which was reportedly followed by a fierce gun battle between security forces and militants.

Officials said those injured in the attack were taken to a nearby hospital. Some are reported to be in a critical condition.

No group has yet claimed responsibility for the attack but the Taliban is known to oppose polio schemes, which it sees as a cover for international espionage.

The attack is the latest in a series of violent assaults against health workers in Pakistan who are accused of being part of a Western plot to sterilise Muslims.

More than 40 vaccination workers have been killed in Pakistan since December 2012. Last month, three polio workers were shot dead by unidentified gunmen in the southern city of Karachi a day after a new nationwide vaccination drive was launched by authorities.

Pakistan is one of only three countries, alongside Afghanistan and Nigeria, where polio remains endemic. The World Health Organisation (WHO) has warned that Pakistan's northwest city of Peshawar is the world's "largest reservoir" of polio.

According to WHO figures, Pakistan recorded 91 cases of polio last year – up from 58 in 2012.