HERAT, Afghanistan - At least four civilians were killed and 12 others including three policemen were injured Saturday morning when a bomb targeted a police vehicle blasted in western Afghan province of Herat, an official said.

"A bomb was placed under a small bridge and was detonated when a police vehicle was running the area in Shindand district bazaar at around 8:00 am local time Saturday, leaving the casualties," a provincial government spokesman, Mahyoddin Noori, told Xinhua.

He said the injured were shifted to a district hospital and an injured policeman was in critical condition.

He blamed Taliban insurgents for the attack.

The Taliban-led insurgency has been rampant since the militant group launched an annual spring offensive dubbed "Al-Farooq" from May against Afghan and NATO-led troops stationed in the country.

The Taliban insurgents has warned the civilians to stay away from official gatherings, military convoys and centers regarded as the legitimate targets by militants besides warning people against supporting government and foreign troops.

A total of 1,145 civilians were killed and 1,954 injured in conflict -related violent incidents and attacks in the first six months of 2012, a 15 percent decrease in overall civilian casualties compared with the same period in 2011, according to a UN report released in capital Kabul on Aug 8.