In Pakistan, a bomb went off near a police check post in the suburbs of Peshawar on Thursday, injuring four persons, including three policemen.The timed explosive device was planted beneath a bridge close to the check post near the Peshawar University. Ambulances rushed to the site to take the injured to nearby hospitals.Meanwhile at least 12 militants, including two key commanders, have been gunned down and 180 suspects arrested by troops in Pakistan's restive Swat valley, where a fresh crackdown was launched against insurgents following the killing of an NWFP legislator in a suicide blast two days ago.