**At least four policemen have been killed after gunmen ambushed a police patrol van in north-west Pakistan , officials say.**The attack took place in Bara district on the outskirts of Peshawar city.
Police said about 10 attackers were hiding on both sides of the road and opened fire as the police van passed. Two officers died on the spot.
Elsewhere, a roadside bomb detonated in the semi-tribal district of Bannu killed a security official there.
The attack targeted a vehicle of the Frontier Constabulary.
Seven other officers were wounded in the attack, news agency Associated Press quoted a local hospital official as saying.
No group has claimed responsibility for either of the attacks, but Taliban militants active in north-west Pakistan regularly target security forces.