Total Curfew in Baghdad

As bad as things have been in Baghdad, I wonder what threat spawned a 36 hour TOTAL CURFEW. All vehicles and pedestrians prohibited from the streets, citywide.

The Iraqi government has declared an immediate curfew in the capital, Baghdad, to run until Sunday morning. The move affects both vehicles and pedestrians, a spokesman for the Iraqi prime minister said.....

An unidentified official at the interior ministry told the Associated Press news agency that "intelligence information on the security situation" had made the announcement necessary.

This is a big step. There have been car bans periodically, but I don't ever remember a total curfew banning pedestrians.

UPDATE: CNN just reported that the US military was "taken by surprise," and knew nothing about it. Also CNN, the Sunni leadership and internal police had no prior knowledge either.

I would think if it was operational intel either the US or the police would know. A coup threat? But you would think Maliki would run to the Americans in that case.

I have no idea what's going on.