QUETTA, Pakistan -- A powerful bomb attached to a motorcycle exploded near a vehicle carrying police officers assigned to protect polio workers in restive southwest Pakistan on Friday, killing nine people including five nearby children, and wounding 17 other people, officials said. Local police chief Fateh Mohammad said the attack occurred in Mastung, a district in Balochistan province. He said a motorized rickshaw carrying schoolchildren was nearby when the bombing happened, resulting in the deaths of five children, a police officer and two passersby.

Some of the wounded were moved to a hospital in Quetta, the capital of Balochistan province, said Wasim Baig, a spokesman for the health department. He said seven people died on the spot, while two men who had been critically wounded died at a hospital. No one immediately claimed responsibility for the attack on police, but suspicion is likely to fall on separatist groups and Pakistani Taliban that have stepped up attacks on security forces and civilians in recent months.

The police chief in Mastung, Rehmat Ullah, said a police van came under attack when it was heading to a health center to escort polio workers for the door-to-door campaign that began on Monday to vaccinate 45 million children under 5, following a surge in new cases. Pakistan has recorded 41 polio cases across 71 districts so far this year. The latest attack came days after militants attacked a health center used in the ongoing anti-polio campaign in northweste.