Continued from page 1

Workers were able to immunize only about 9 million children this week out of a target of 18.3 million because of the violence, Mr. Durry said.

Polio usually infects children living in unsanitary conditions, attacks the nerves and can kill or paralyze. Pakistan, Afghanistan and Nigeria remain the last battlegrounds for the fight against the disease.

There is no history of attacks on polio workers in Afghanistan, even though the country also faces a domestic Taliban insurgency. Muslim leaders in Nigeria have spoken out against polio vaccination in the country in the past, also claiming it makes children sterile. Many now support the campaign, but some Nigerians remain suspicious.

Prevention efforts have managed to reduce the number of cases in Pakistan to 56 this year, compared with 190 in 2011, a drop of about 70 percent. Most of the news cases in Pakistan are in the northwest, where the presence of militants makes it difficult to reach children. Clerics and tribal elders have been recruited to support polio vaccinations to try to open up areas previously inaccessible to health workers.

Israrullah Khan, a villager who attended the funeral of the polio worker who died Thursday, said most of the clerics and Islamic political parties in Khyber Pakhtunkhwa were in favor of the campaign.

“We don’t understand why these attacks have suddenly started,” Mr. Khan said. “It’s very sad because they were trying to save our children’s future for very low wages.”

• Associated Press writers Jamal Khan in Peshawar, Pakistan; Zaheer Babar in Lahore, Pakistan; Adil Jawad in Karachi, Pakistan; and Munir Ahmed in Islamabad contributed to this report.