The attackers, who were in a car, fired indiscriminately at the police van that was on a routine patrol.
Two policemen were killed instantly. Officials described the condition of the two injured policemen as serious.
The attackers fled after the shooting. Security forces cordoned off the site of the attack and launched a search operation.
No group claimed responsibility for the incident though such attacks are usually blamed on Baloch national groups.
Islamabad: Suspected militants opened fire at a police van on the outskirts of Quetta city in southwest Pakistan on Thursday, killing two policemen and injuring two more, officials said.
First Published: Thursday, May 17, 2012, 13:31