Suspected militants opened fire on a police vehicle in northwest Pakistan on Tuesday, killing four officers before fleeing, officials said, part of a surge in violence in the region bordering Afghanistan.

Axar.az informs, citing AP, the attack took place in the Karak district of Khyber Pakhtunkhwa province while police were on routine patrol near an oil and gas field, said local police chief Noor Wali. A large police contingent cordoned off the area and launched a search operation to track the attackers.

Pakistan’s Interior Minister Mohsin Naqvi and Khyber Pakhtunkhwa Chief Minister Suhail Afridi condemned the attack. In separate statements, they said the assailants would be brought to justice and expressed condolences to the families of the killed police officers.

No group immediately claimed responsibility, but suspicion is likely to fall on the Pakistani Taliban, or TTP, which is separate from but aligned with Afghanistan’s Taliban government and has been blamed by authorities for previous attacks.