The U.S. military says mortar fire caused a massive fire at an ammunitions depot at a U.S. base in Baghdad late Tuesday.

A U.S. military spokesman, Lt. Col. Jonathan Withington, says intelligence suggests that civilians aligned with a militia group were responsible for the attack.

The fire ignited tank and artillery ordnance. Plumes of smoke were seen rising from the depot for hours. No casualties were reported.

In violence Wednesday in Iraq, at least four people were killed in three car bomb attacks in the capital.

Also Wednesday, the Iraqi parliament approved a law that would allow the country's 18 provinces to hold referendums on forming federal regions.

Meanwhile, the genocide trial of Saddam Hussein continues, one day after the former Iraqi leader was expelled from the courtroom for disruptive behavior.

Saddam and his six co-defendants are accused of carrying out a campaign of genocide against Iraqi Kurds in the 1980s. Prosecutors say 182,000 Kurds were killed.

The witnesses have told the court about rapes, killings and other abuses at the hands of Saddam's forces. Saddam and his six co-defendants face the death penalty if convicted.

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