Baghdad, Iraq ? Iraqi authorities discovered at least 87 corpses – men shot to death execution-style – as Iraq edged closer to open civil warfare. Twenty-nine of the bodies, dressed only in underwear, were dug out of a single grave Tuesday in a Shiite neighborhood of Baghdad.

Some of the bloodshed appeared to be retaliation for a bomb and mortar attack in the Sadr City slum that killed at least 58 people and wounded more than 200 two days earlier.

Plot foiled

Iraq’s Interior Minister Bayan Jabr, meanwhile, told The Associated Press security officials had foiled a plot that would have put hundreds of al-Qaida men at critical guard posts around Baghdad’s heavily fortified Green Zone, home to the U.S. and other foreign embassies, as well as the Iraqi government.

A senior Defense Ministry official said the 421 al-Qaida fighters were recruited to storm the U.S. and British embassies and take hostages. Several ranking Defense Ministry officials have been jailed in the plot, said the official, speaking on condition of anonymity because of the sensitivity of the information.

Defense Secretary Donald H. Rumsfeld said Tuesday that he had not received anything definitive on the report, but cautioned that earlier accounts are often adjusted later on.

Unidentified masked gunmen fire at a government building Tuesday in Ramadi, 70 miles west of Baghdad, Iraq. Gunmen fired three mortar rounds targeting a U.S base and a government building.

“We’ve always known that there are people who have tried to infiltrate the various security forces and tried to get close access to places that they ought not to be,” he said. “There’s nothing new about that that I know of.”

Gruesome findings

Police began unearthing bodies early Monday, although the discoveries were not immediately reported. The gruesome finds continued throughout the day Tuesday, police said, marking the second wave of sectarian retribution killings since bombers destroyed an important Shiite shrine last month.

In the mayhem after the golden dome atop the Askariya shrine in Samarra was destroyed on Feb. 22, more than 500 people have been killed, many of them Sunni Muslims and their clerics. Dozens of mosques were damaged or destroyed.

The most gruesome find Tuesday – the 29 bodies dressed only in underwear – was made after police, acting on a tip, discovered an 18-by-24-foot grave in an empty field in Kamaliyah, a mostly Shiite east Baghdad suburb, Interior Ministry official Lt. Col. Falah al-Mohammedawi said. He estimated the victims were killed about three days ago – before the Sadr City attack Sunday evening.

Residents watched, some covering their eyes in horror, others offering scarves and newspapers to cover the bodies as they were pulled from the grave.

Driving ban announced

Underlining the unease in the capital, Interior Ministry officials announced another driving ban, from 8 p.m. today to 4 p.m. Thursday, to protect against car and suicide bombs while the Iraqi parliament meets for the first session since the Dec. 15 election.

After the driving ban was announced, the Cabinet said Thursday would be a holiday in the capital, presumably because residents would not be able to get to work. Restrictions on movement also had been put in place on the two weekends after the Samarra bombing in an attempt to quell the violence.

An abandoned minibus containing 15 other bodies was found earlier on the main road between two mostly Sunni west Baghdad neighborhoods – not far from where another minibus containing 18 bodies was discovered last week, al-Mohammedawi said.

At least 40 more bodies were recovered elsewhere in Baghdad, in both Sunni and Shiite neighborhoods, al-Mohammedawi said. Police found three other corpses dumped in the northern city of Mosul.

The sectarian violence has complicated negotiations for Iraq’s first permanent, post-invasion government. A caretaker government has been in charge since the December elections and U.S. and Iraqi officials fear the vacuum in authority has fueled the bloodshed.