A wave of bombings tore through Baghdad on Tuesday morning, killing at least 56 people and wounding more than 200, highlighting increasing sectarian tensions in Iraq on the eve of the anniversary of the U.S.-led invasion.

The attacks, mostly by car bombs, targeted small restaurants, day laborers and bus stops in the Iraqi capital and nearby towns over a span of more than two hours.

The bombings came 10 years to the day that Washington announced the start of the invasion on March 19, 2003 _ though by that time it was already the following morning in Iraq.

While violence has ebbed since its peak in 2006 and 2007, the latest attacks show that insurgents remain a potent threat to Iraq's security forces and long-term stability.

One of the deadliest of Tuesday's attacks struck close to one of the main gates to the heavily-fortified Green Zone, which houses major government offices and the embassies of several countries, including the United States and Britain. That blast outside a restaurant killed six people, including two soldiers, and wounded more than 15. Thick black smoke could be seen rising from the area as ambulances raced to the scene.

There was no immediate claim of responsibility for Tuesday's blasts, but the attacks bore hallmarks of al-Qaida in Iraq. The terror group favors spectacular, coordinated bombings intended to undermine public confidence in the Shiite-led government.

Police and hospital officials who provided accounts of the days' bloodshed reported the most casualties from a car bombing near the Ministry of Labor and Social Affairs in Baghdad's eastern Qahira neighborhood at around 10 a.m. That blast killed seven people and wounded 21.

The officials provide casualty numbers on condition of anonymity because they were not authorized to release the information to journalists.

The violence started at around 8 a.m., when a bomb exploded outside a popular restaurant in Baghdad's Mashtal neighborhood, killing four people and wounding 15. It blew out the eatery's windows and left several cars mangled in the blood-streaked street.

Minutes later, two day laborers were killed and eight were wounded when a roadside bomb hit the place where they gather every day in an area of New Baghdad.

In the poor Shiite neighborhood of Sadr City, a bomb stuck to the underside of a minibus killed three commuters and wounded seven people. Another car bomb exploded in a commercial street in the same area, killing two people and wounding 11, and yet another bomb struck a police patrol in the neighborhood, killing five people and wounding 13.

Other attacks struck the largely Shiite neighborhoods of Hussainiyah, Zafarniyah, Shula and Utaifiya, as well as the Sunni district of Tarmiyah.

Just outside the capital, a mortar shell landed near a clinic in the town of Taji, killing two people and wounding five. And about 50 kilometers (30 miles) south of Baghdad, in Iskandiriyah, a car bomb exploded near a bus stop, killing five people and wounding 20 others.

Tuesday's attacks came a day after insurgents killed nine people, including a bombing by a suicide attacker who killed five when he drove an explosives-laden car into a checkpoint in the central Iraqi town of Balad Ruz.

Al-Qaida's Iraq arm, which operates under the name the Islamic State of Iraq, has sought to re-assert its presence in recent weeks.

Last week, the group claimed responsibility for a highly coordinated attack earlier this month in far western Iraq that killed nine Iraqis and 51 Syrian soldiers who had sought temporary refuge in the country.

And on Sunday, al-Qaida's Iraq branch took responsibility for a brazen and again highly coordinated raid on the Justice Ministry in downtown Baghdad last week. The attack, involving car bombs and gunmen disguised as police, killed at least 24 people.

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Associated Press writers Sameer N. Yacoub, Qassim Abdul-Zahra and Sinan Salaheddin contributed to this report.