Gunmen on motorbikes shot dead five female Pakistani polio vaccination workers on Tuesday, police said, highlighting resistance to the country's immunisation campaign.
Four were killed in three different incidents in the sprawling port city and the fifth in the northwestern city of Peshawar, on the second day of a nationwide three-day drive against the disease, which is endemic in Pakistan.
Sagheer Ahmed, the health minister for Sindh province, of which Karachi is capital, said he had ordered a halt to the anti-polio drive in the city in the wake of the shootings.
Senior Karachi police officer Shahid Hayat said another polio worker was shot dead in the city on Monday, but the circumstances of his death only became clear on Tuesday.
In Peshawar, which lies close to the restive tribal areas, a haven for militants and hotspot for polio, two attackers on a motorbike fired on two sisters working on vaccination, killing one, senior police official Javed Khan told AFP.
The incident took place in Mathra suburb of Peshawar which borders Mohmand tribal district, Khan said.
Hayat blamed "militants who issued a fatwa against polio vaccination in the past" for the Karachi killings.
Pakistan is one of only three countries where the highly infectious crippling disease remains endemic, along with Afghanistan and Nigeria.
But efforts to tackle polio have been hampered over the years by suspicion over vaccination drives.
The Taliban have banned immunisations in the northwest, condemning the campaign as a cover for espionage since a Pakistani doctor was jailed after helping the CIA find Osama bin Laden using a hepatitis vaccination programme.
The ban -- to protest against US drone strikes and because they allege that the anti-polio campaign is a cover for espionage -- risks the health of 240,000 children in North and South Waziristan tribal areas, officials say.
Tuesday's killings in Karachi took place in parts of the city dominated by Pashtuns, Hayat said. Pashtuns are the dominant ethnic group in northwest Pakistan and have a sizeable migrant population in Karachi.
WHO, a partner in government efforts to eradicate the disease, suspended vaccination activities in part of Pakistan's largest city in July after a spate of bloody shootings.
A UN doctor from Ghana working on polio eradication and his driver were shot in part of Karachi and three days later a local community worker who was part of the same campaign was shot dead in the same area.