Homicide bombers struck Tuesday across the street from the heavily guarded Green Zone, killing up to 16 people — the deadliest attack in a wave of bombings and shootings that threatened to shatter confidence in Iraq's new national unity government.

In all, about 60 people died in more than a dozen bombings, shootings and ambushes — mostly in the Baghdad area, according to police reports. The dead included 10 Shiites who were killed when gunmen fired on their bus as it left the capital for a funeral in southern Iraq, police said.

CountryWatch: Iraq

Lawmakers summoned the defense and interior ministers to explain the failure of Prime Minister Nouri al-Maliki's security plan for the capital — where most of the recent violence has occurred.

The attack near the Green Zone occurred at midmorning when two suicide bombers detonated their explosives at a restaurant frequented by police, the U.S. military and witnesses said.

Sixteen other people were killed in the blast, the U.S. military said. Iraqi police put the casualty figure at 12 dead and 13 wounded. Blue-uniformed Iraqi police hauled the dead from the wreckage in body bags as heavily armed American soldiers stood guard nearby.

A statement posted on an Islamist Web site in the name of the Islamic Army in Iraq claimed responsibility for the attack, saying it was in retaliation for Israeli military operations in Gaza and the alleged rape-slaying by U.S. soldiers of a young Iraqi woman south of Baghdad.

The Islamic Army is a major insurgent group but authenticity of the statement could not be determined.

Much of the violence Tuesday appeared sectarian, part of a surge in tit-for-tat killings that began Sunday when Shiite gunmen rampaged through a mostly Sunni area of west Baghdad, killing 41 people, according to police.

Throughout Tuesday, car bombs detonated and mortar shells exploded in Shiite and Sunni neighborhoods across the sprawling capital. Most caused few deaths and injuries but collectively the toll was horrific, suggesting that U.S. and Iraqi forces are powerless to stop the violence soon.

As night fell, police reported explosions and gunfire in the western Baghdad neighborhood of Amariyah. Bursts of heavy machine gun fire could be heard intermittently late Tuesday from along the Tigris River that flows through the center of the city.

The United States had hoped that a unity government of Shiites, Sunnis and Kurds could calm sectarian tensions, convince insurgents to lay down their arms so that U.S. and its coalition partners could begin withdrawing troops starting this year.

But more than 1,607 Iraqis have been killed and nearly 2,500 wounded since al-Maliki's unity government took office on May 20, according to an Associated Press count.

Alarmed by the crisis, Iraq's parliament summoned Interior Minister Jawad al-Bolani and Defense Minister Abdul-Qader al-Obeidi to appear Thursday to discuss the "deteriorating security situation," deputy speaker Khaled al-Attiyah said.

Last month al-Maliki's government unveiled a sweeping plan to restore security in Baghdad, putting tens of thousands Iraqi and U.S. troops on the streets, increasing the number of checkpoints and stepping up patrols in selected neighborhoods.

Many Iraqi lawmakers and media commentators have complained that the plan has done little except tie-up traffic at checkpoints, forcing ordinary people to sit for hours in their cars under the sweltering summer sun.

"The security plan did not succeed. There must be solutions found for this situation, which is out of control," Kurdish legislator Mahmoud Othman told reporters.

The Shiite head of parliament's security committee, Hadi al-Amiri, said the security plan will be reviewed as soon as possible because the situation in Baghdad is "the worst in three years."

But al-Maliki, on a tour of northern Iraq, played down fears of civil war, telling reporters in the Kurdish city of Irbil that "the people of Iraq will not allow that to happen."

In a rare sign of accommodation, Sunni legislators agreed Tuesday to end their boycott of parliament following a call for reconciliation by radical Shiite cleric Muqtada al-Sadr and promises that a kidnapped colleague will be released.

The Iraqi Accordance Front suspended its participation in parliament this month after one of its members, Tayseer al-Mashhadani, was kidnapped in a Shiite neighborhood in Baghdad. Many Sunnis blamed Sadr's Mahdi Army militia, although the organization has denied any involvement.

"We have decided to attend the meetings as of tomorrow in response to the call by Muqtada al-Sadr," lawmaker Adnan al-Dulaimi told The Associated Press. Two of al-Mashhadani's guards were released last week.

In other violence Tuesday:

— Gunmen killed five Iraqi employees of a Saudi Arabian import/export company in the upscale Mansour neighborhood.

— An Iraqi diplomat on leave from his post in Iran was kidnapped from his west Baghdad home, police said. Iraq's Foreign Ministry said Wissam Jabr al-Awadi was a consul in the Iranian city of Kermanshah.

— Gunmen killed 10 members of a special force protecting oil installations near Sharqat, 45 miles south of Mosul, police said. In Baqouba, gunmen in a speeding car fired randomly at textile shops, killing two shop owners and wounding four others, police said.