A bomb-laden car exploded Saturday in northwestern Pakistan as police were trying to pull a body from it, killing seven policemen and a passer-by, authorities said. It appeared to be the first time militants in Pakistan had targeted security forces by using a body as a lure, and it underscored the challenge facing Pakistan as it tries to root out al-Qaida, Taliban and other insurgents based along its border with Afghanistan. The Saturday morning explosion comes less than a week after gunmen attacked Sri Lankan cricket players in eastern Pakistan and amid rising political turbulence from a court decision to bar an opposition leader from office. The explosion occurred in the Badaber area, a small town on the outskirts of the main northwest city of Peshawar, where residents recently evicted a group of militants with help from the police. The move prompted militant threats of retaliation.