KHAR, Pakistan (AP) — An officer critically wounded in a roadside bombing that targeted police assigned to protect polio vaccination workers in northwest Pakistan died in a hospital Tuesday, raising the death toll to seven.

Police said in a statement that at least three officers remained in critical condition after Monday’s bombing in Mamund, a former stronghold of the Pakistani Taliban in Khyber Pakhtunkhwa province bordering Afghanistan.

The militant group claimed responsibility for the attack.

Pakistan and Afghanistan are the only countries in the world where polio remains endemic.

Monday’s bombing in Mamund happened after the government began another round of its regular vaccination drives. Islamic militants often target the polio teams and police assigned to protect them, claiming falsely that the vaccination campaigns are a Western conspiracy to sterilize children.

The vaccination drive in Mamund was suspended for a second day Tuesday.