PESHAWAR, Pakistan (AP) — Four Pakistani police officers were killed and another four critically wounded Sunday when suspected militants attacked a police station in the country's volatile northwest, police said.

The suspects used grenades and automatic weapons on the station in Lakki Marwat district before fleeing the scene overnight, said Nawaz Khan, an officer of the targeted police station.

Khan said police on duty retaliated and called for reinforcement before the attackers, their ammunition apparently exhausted, fled the scene before help arrived. Police were searching for the attackers.

No group immediately claimed responsibility for the attack, but previous attacks on police in the district have been claimed by Pakistani Taliban, also known as Tehreek-e-Taliban Pakistan, TTP.

Last month, militants ambushed a routine police patrol, killing all six policemen in the vehicle in the Dadewala area of the Lakki Marwat district. The Pakistani Taliban claimed responsibility for the Dadewala ambush. The militant group is separate but allied with the Afghan Taliban.

A suicide bomber blew himself up near a truck carrying police officers on their way to protect polio workers near Quetta, in southwestern Pakistan late last month, killing a police officer and three family members traveling in a car nearby. The bombing wounded 23 others, mostly police.

Both southwestern Baluchistan and northwest Khyber Pakhtunkhwa province borders Afghanistan, where Taliban rule last year emboldened Pakistani Taliban.