Gunmen in Pakistan have shot and killed a polio worker – the third death this week linked to the country's latest vaccination drive, government officials said.

The latest attack happened on Thursday in the south west city of Chaman, which borders Afghanistan, when two female vaccination workers were targeted as they carried out an immunisation programme.

Nasreen Bibi, 35, was killed instantly, while a 24-year-old woman – named only as Rashida – was seriously wounded.

The attackers are still at large and officials have temporarily suspended the anti-polio drive following the incident.

Rashid Razzaq, an official at the government polio emergency center in provincial capital of Quetta, said: "Two gunmen opened fire on two female polio vaccinators in Sultan Zai village, located about 100km north west of the Baluchistan provincial capital Quetta. Nasreen Bibi 35, died at the spot while Rashida 24 is seriously injured."