PESHAWAR, Pakistan — Two volunteers in a polio immunization campaign were shot to death on Sunday in the Swabi district of northeastern Pakistan, the police said.

The shootings occurred in the hilly village of Pebani, in the northeastern fringes of the district. The two volunteers, one a local schoolteacher, were killed by two gunmen, the district police chief, Mian Saeed, said.

“The gunmen were on foot,” he said. “They shot dead the two workers from close range and escaped. Four suspects have been rounded up for questioning.”

It was the second attack on polio workers in the district. A police constable accompanying a polio team was killed in January. Militants believe that polio vaccination is against Islamic law.