ISLAMABAD, June 25 (Xinhua) -- Two policemen were killed and four others injured when some unknown insurgents fired at a police vehicle in Pakistan's northwest Nowshera district, local media reported Tuesday evening.

The policemen were on their routine patrol in the city when their vehicle was attacked by the assailants in the country's Khyber Pakhtunkhwa province, the reports said.

The injured policemen were taken to the Lady Reading Hospital in the provincial capital of Peshawar, where hospital officials said that the death toll might rise as two of the wounded are in critical condition.

No group or individual has claimed responsibility for the attack yet.

Police and security forces have cordoned off the attack site for investigations.