PESHAWAR, Pakistan (AP) — A roadside bomb hit a vehicle carrying officers assigned to protect health workers conducting a polio immunization drive in a former stronghold of the Pakistani Taliban in northwestern Pakistan on Monday, wounding six officers and three civilians, officials said.

No polio workers were hurt in the attack in South Waziristan, a district in Khyber Pakhtunkhwa province, local police official Tahrir Sarfraz said.

He said no one has claimed responsibility for the attack, which apparently targeted police.

Anti-polio campaigns in Pakistan are regularly marred by violence. Militants target vaccination teams and police assigned to protect them, falsely claiming that the campaigns are a Western conspiracy to sterilize children.

The latest attack came hours after Pakistan launched a drive to vaccinate 30 million children against polio. Since January, Pakistan has reported 17 new cases, jeopardizing decades of efforts to eliminate polio in the country.

Pakistan and neighboring Afghanistan are the only countries in which the spread of polio has never been stopped.

The potentially fatal, paralyzing disease mostly strikes children under age 5 and typically spreads through contaminated water.