On Christmas Eve in the Green Zone, karaoke is blaring into the night from a contractor's villa while U.S. troops use a sniffer dog to check for car bombs just a block away.

This morning saw the start of perhaps the most extensive security operation I've seen in this fortified home to the Iraqi government and U.S. mission. Army engineers came with cranes and blocked side streets in the 4-square-mile district with concrete barriers. Snap checkpoints (in addition to the usual checkpoints) were mobilized to stop cars and check IDs of pedestrians. There's been an obvious reinforcement of troops, crowding the streets with their convoys of enormous MRAP (mine-resistant ambush protected) armored trucks, all causing gossip and speculation among the thousands of American and Iraqi residents who live in the big compounds, apartment blocks and suburban-style streets.