Gunmen killed three health workers taking part in a polio vaccination drive in Karachi on Tuesday (January 22), police said, in the latest blow to efforts to stamp out the disease in Pakistan.

After the attacks, the latest in a series of deadly assaults on vaccination teams, the provincial polio workers' association said it was halting operations across Sindh province.

According to reports, assaliants were riding on bike as they opened fire on polio teams in two separate incidents in the Qayyumabad neighbourhood.

Pakistan is one of only three countries in the world where polio remains endemic, along with Afghanistan and Nigeria.

Efforts to eradicate it have been seriously hampered by the deadly targeting of vaccination teams in recent years.

No one has claimed responsibility for the attack so far.

Militant groups see vaccination campaigns as a cover for espionage.