Sixteen people died in Baghdad's Sadr City as fresh clashes broke out between security forces and Shiite militiamen in the capital on Wednesday, the fifth anniversary of the fall of Baghdad.

The city's Green Zone, which houses diplomatic missions and much of Iraq's government, also came under renewed attack by rockets or mortars early Wednesday. The U.S. embassy confirmed the shelling, but said there were no immediate reports of casualties.

The bloodshed served as stark reminders of Iraq's continuing instability five years after U.S. troops swept into Baghdad and toppled Saddam Hussein's regime on April 9, 2003. The euphoria of victory soon dissipated — pummeled first by a Sunni insurgency, then Sunni-Shiite slaughter and now battles against Shiite militiamen.

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Police said the seven of the victims in Sadr City — including three children — died when projectiles slammed into a house in the sprawling slum, a stronghold of the Mahdi Army militia of anti-American cleric Muqtada al-Sadr.

Twenty-seven other people were wounded, said a hospital official who asked not to be identified because he was not authorized to speak to the media. Police said the blasts were caused by mortar rounds.

In another incident, a mortar shell crashed into a nearby residential area in the district around noon, killing seven people and wounding 36 others, police and hospital officials said.

The U.S. military said one of its drones launched a Hellfire missile during the night at two gunmen shooting at government forces in a different part of Sadr City. Both men were killed, a statement said.

The military also announced that U.S. special forces uncovered a large weapons cache last week in the Jazeera Desert in northwestern Iraq. The arms, located in an abandoned Iraqi air force radar station, included shoulder-launched SA-7 surface-to-air missiles, rockets, heavy machine guns, mortars, ammunition and hand grenades.

As tension rose in Baghdad on the eve of the anniversary, the Iraqi military ordered vehicles and motorcycles off the streets 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.

On Tuesday, Iraqi military spokesman Brig. Gen. Qassim al-Moussawi said a total of 82 militants, 36 civilians and 37 soldiers had been killed since March 16 in fighting in Baghdad, mostly in Sadr City.

The U.S. military announced Wednesday that two American soldier had died, one from non-combat related injuries and one in a roadside bomb attack.

At least 14 American service members have died in Iraq since Sunday, and the shelling of the Green Zone has become almost a daily occurrence.

In Washington, U.S. commander Gen. David Petraeus called Tuesday for an open-ended suspension of U.S. troop withdrawals this summer because of concern over the renewed fighting.

As the number of U.S. forces in Iraq has gradually come down in the past three months, the number of high-profile car bomb and suicide attacks, weekly security incidents, civilian casualties and episodes of ethno-sectarian violence has gone up.

In his testimony to a congressional committee, Petraeus refused to give any indication that more troops could leave Iraq this year, after the last of five brigades ordered into the country for the buildup last year have come home. About 140,000 U.S. troops, including 15 brigades, are expected to be in Iraq at the end of July, down from the roughly 160,000 there now.