LAHORE, Pakistan — Under police guard, thousands of health workers pressed on with a polio immunization program Thursday after nine were killed in Pakistan by suspected militants who oppose the vaccination campaign.
Immunizations were halted in some parts and the United Nations suspended its field participation everywhere until better security was arranged. The violence risks reversing recent progress fighting polio in Pakistan, one of three countries where the disease is endemic.
The Taliban have denied responsibility for the shootings. Militants have accused health workers of acting as spies for the United States, alleging the vaccine is intended to make Muslim children sterile.
Taliban commanders in Pakistan’s troubled northwest tribal region said this year that vaccinations cannot go forward until the United States stops drone strikes.
Insurgent opposition to the campaign grew last year after it was revealed that a Pakistani doctor ran a fake vaccination program to help the CIA track and kill Osama bin Laden, in the country’s northwest.
There were a few attacks on polio workers in July, but the current level of violence is unprecedented. A polio worker died Thursday after he was shot in the head in the northwestern city of Peshawar a day earlier, said health official Janbaz Afridi.
His death raised to nine the number of Pakistanis working on the campaign who have been killed this week. Six were women, three of whom were teenagers. Two other workers were critically wounded. The attacks were in northwest Khyber Pakhtunkhwa Province and the southern city of Karachi.
Despite the threat, officials in the eastern city of Lahore continued the vaccination drive under police escort. About 6,000 health workers were escorted by 3,000 police as they fanned out across the city.
‘‘It would have been an easy thing for us to do to stop the campaign,’’ said an official, Noorul Amin Menga. ‘‘That would have been devastating.’’
Saddaf Malik, one of the polio workers in Lahore, said the killings sent fear through him and his colleagues.
‘‘We will carry on with our job with determination, but we want the government to adopt measures to ensure the security of polio vaccinators,’’ he said.
This week’s killings occurred as the government and the UN began a vaccination drive Monday targeting high-risk areas in the country’s four provinces and the semiautonomous tribal region, part of an effort to immunize 34 million children under age 5. The campaign was scheduled to end Wednesday in most parts, except for Lahore, where it ran a day longer.
Government officials ended the drive early in parts of Khyber Pakhtunkhwa and in Sindh Province, where Karachi is the capital, said Elias Durry, the UN World Health Organization’s senior coordinator for polio in Pakistan. The campaign ran its full course in the provinces of Baluchistan and Punjab, where Lahore is the capital, as well as in the tribal region.
The government has approximately 250,000 people working on the campaign, said Durry. Most of them have other jobs, such as teaching or working as government clerks, and sign on to the vaccination drive to earn a little more money, about $2.50 per day.