Peshawar, Pakistan (CNN) — Two vans carrying a polio vaccination team were hit by a roadside bomb in Pakistan’s northern Khyber Agency on Saturday, authorities said.

The attack killed at least six people and injured 12, they said.

Security forces and militants at the scene were engaged in a gun battle.

The Khyber Agency is a loosely governed tribal region, which borders on Afghanistan.

Pakistan’s military has been carrying out operations against suspected Taliban strongholds in Khyber and other nearby agencies, after peace talks with the militant group broke down.

Earlier this week, government airstrikes demolished suspected Pakistani Taliban hideouts in Waziristan and may have killed dozens, the military said.