US troops sweep Baghdad in 'security crackdown'

Thousands of US troops swept house-to-house through mostly Shi'ite areas near a militia stronghold Wednesday in the opening phase of the long-awaited Baghdad security crackdown. The clearing operation began as Iraqi forces set up new checkpoints across the city of 6 million people, snarling traffic and forcing Iraqis to stream across bridges on foot. The neighborhoods targeted by the Americans are north of the Shi'ite militia stronghold of Sadr City, which had been off-limits until Prime Minister Nouri al-Maliki lifted his protection of them.