ISLAMABAD: Gunmen have shot dead five health workers in Pakistan at the start of a polio vaccination drive, in a spree of apparently co-ordinated attacks on the nationwide medical campaign.

Officials were forced to halt the three-day vaccination programme in Karachi after four women were shot dead in the city in less than an hour.

The assassinations follow a Taliban ban on immunisations in the tribal region of Waziristan. The militants say the ban is in protest against drone strikes and also allege that the immunisation campaign is a cover for spying.

The four women were killed a day after a man working on a World Health Organisation project was shot and wounded in the city, police told reporters.