Unauthorized vehicles will be banned in Baghdad from 5 a.m. to midnight on Wednesday, the fifth anniversary of the city's capture by U.S. troops.

Iraqi state TV announced that Iraqi military command authorized the curfew in baghdad. Pedestrians will be allowed to travel on foot

Shiite cleric Muqtada al-Sadr is threatening to lift a seven-month freeze on his Mahdi Army militia if the Iraqi government does not halt attacks on his followers or set a timetable for a U.S. withdrawal.

On the eve of the anniversary, the Baghdad military command ordered vehicles and motorcycles off the streets of the capital from 5 a.m. Wednesday until midnight — a move apparently aimed at preventing Shiite gunmen from moving freely about the city.

The vehicle ban was imposed despite a decision by al-Sadr to call off his "million-strong" demonstration set for Wednesday to demand an end to the American military presence. Al-Sadr's Mahdi militia has been battling American and Iraqi soldiers in the capital's Sadr City district.

Fearing the demonstration might trigger violence throughout Baghdad, Iraqi soldiers began turning back military-aged men traveling to the capital Tuesday from Shiite areas to the south.

Al-Sadr then called off the rally, apparently fearing a modest turnout would display weakness at a time when he is locked in a violent power struggle with Prime Minister Nouri al-Maliki, a fellow Shiite. Al-Maliki has told al-Sadr to disband his militia or give up politics.

Instead, al-Sadr's aides called a news conference at a hotel on Firdous Square, where U.S. Marines hauled down the statue of Saddam five years ago, and released a statement condemning the government for allegedly bowing to "the hated American pressure."

"I call on the Iraqi government, if it exists, to work to protect the Iraqi people, stop the spilling of its blood, and the abuse of its honor," al Sadr said in the statement.