Militiaman holding rocket-propelled grenade runs in street of Sadr City, Baghdad, 09 Apr 2008

Iraqi officials say at least 13 people have been killed in Baghdad's Sadr City district despite increased security on the fifth anniversary of the fall of Baghdad to U.S. forces.

Police say an explosion in the Shi'ite neighborhood Wednesday killed seven people and wounded more than 14 others. Overnight, mortar shells killed at least six people and wounded at least 24.

It is unclear who was responsible for the attacks. The district has been the scene of increased fighting between U.S. forces and militants loyal to radical Shi'ite cleric Moqtada al-Sadr.

Separately, the U.S. military announced the deaths of two more American soldiers, raising the toll to at least 13 killed since Sunday.

The Iraqi government has imposed a one-day curfew on Baghdad today, banning cars and motorcycles from the streets from five in the morning to midnight local time (2100 UTC).

On Tuesday, Sadr announced he was canceling an anti-U.S. demonstration in Baghdad planned for today, out of concern his followers would be attacked.

Sadr also has threatened to lift a seven-month-old cease-fire by his Mahdi Army militia that has been credited with a sharp overall reduction in violence.

Fighting has intensified in Iraq since Iraqi Prime Minister Nouri al-Maliki ordered a crackdown on Shi'ite militias last month.

Some information for this report was provided by AFP, AP and Reuters.