ISLAMABAD, Feb. 22 (Xinhua) -- At least one policeman was killed and four others were injured when some unknown gunmen sprayed bullets on them in Rawalpindi of Pakistan's Punjab province Thursday night, police sources told Xinhua.

The policemen stopped a suspicious motorbike carrying two people on a check post, when they opened fire at them before fleeing from the scene.

The injured policemen were shifted to a nearby hospital where three of them are in critical condition, the sources added.

Heavy contingent of police arrived at the attack site following the incident and a search operation was kicked off in the adjoining areas to nab the on-the-run miscreants.

No group or individual has claimed the attack yet.