Murders raise to nearly 20 the number of health workers killed on campaign to help rid Pakistan of endemic disease

Gunmen have killed two anti-polio health workers in north-west Pakistan, police said on Sunday, in the latest violence directed at efforts to eradicate the endemic disease from the country.

Two attackers shot the Pakistani health workers, who were on a vaccination drive in Kandar village, said Swabi district police chief, Mohammad Saeed. The gunmen arrived on foot and later disappeared, he added.

No one claimed responsibility for the attack. But some militant groups oppose the vaccinations and accuse the workers of spying for the US. They point out the case of the CIA using a Pakistani doctor to collect blood samples from the family of Osama bin Laden in order to track him down and kill him in Pakistan in 2011.

Militants also try to block inoculation campaigns by portraying them as a conspiracy to sterilise and reduce the world's Muslim population. Over the past year, nearly 20 health workers from the anti-polio campaign have been murdered.

Pakistan is one of three countries, along with Afghanistan and Nigeria, that is still affected by polio, with 58 cases reported in 2012, down from 198 in 2011. The World Health Organisation said in March that some 240,000 children have missed polio vaccinations because of security concerns in Pakistan's tribal regions bordering Afghanistan.

It said the health workers have not been able to immunise children in the Taliban strongholds of North and South Waziristan since July 2012.The shootings came a day after the Pakistani al-Qaida-linked militant group Lashkar-e-Jhangvi killed 24 people in the southwestern city of Quetta.

In the first of Saturday's attacks in Quetta, a blast ripped through a bus carrying female students, killing 14. When the victims were taken to the nearby hospital, a suicide bomber struck there. Other attackers captured parts of the complex, triggering a siege by security forces in which four paramilitaries also died.