BAGHDAD - U.S. forces battled Iraqi police and gunmen Friday, killing six policemen, after an American raid captured a police lieutenant accused of leading an Iranian-backed militia cell, the military said. Seven gunmen also died in the fight, a rare open street battle between American troops and policemen. Washington has demanded the government purge its police force of militants, and U.S. and Iraqi authorities have arrested officers in the past for militia links. But the Bush administration said in an assessment Thursday that progress on that front was "unsatisfactory." The lieutenant was captured before dawn in eastern Baghdad, but the...