BAGHDAD (AP) _ Mortar rounds hammered the U.S.-controlled Green Zone for a second day Wednesday, killing at least two people, wounding about 10 more and raising new fears for the safety of workers at the nerve center of the American mission in Iraq.
About a dozen shells crashed into the 3.5-square-mile area of central Baghdad about 4 p.m., sending terrified pedestrians racing for the safety of concrete bunkers.
Motorists abandoned their cars and sprinted for cover. Sirens wailed and loudspeakers warned people to seek safety.
No American casualties were reported, and the two dead as well as most of the wounded were Iraqis, U.S. Embassy spokesman Lou Fintor said.
An Iraqi security officer said one of the dead was a driver for the staff of Prime Minister Nouri al-Maliki, whose office is in the Green Zone. The officer spoke on condition of anonymity because he was not supposed to release the information.
Both the intensity and skill of the attack were noteworthy. The shells, believed to be 122mm, exploded in rapid succession over about a three-minute period.
The blasts were relatively close to one another, suggesting an experienced mortar crew using more than one launcher.
It was unclear whether the rounds were fired by Sunni or Shiite extremists. Both groups operate in areas of the city within rocket and mortar range of the secured complex despite the ongoing Baghdad security crackdown.
Mortar and rocket crews can set up their weapons quickly on the beds of trucks or in parts of the city with limited surveillance, fire their rounds and flee before U.S. and Iraqi forces can respond.
``When they launch these type of weapons systems, they launch from populated areas, around civilians and in built-up areas,'' Brig. Gen. Perry Wiggins, deputy director of operations for the Joint Chiefs of Staff, told a Pentagon press briefing.
U.S. officials would not comment on damage in Wednesday's attack, citing security.
However, the U.S. Institute of Peace said its office suffered ``significant'' shrapnel damage though there were no casualties among its staff. The institute sponsored the bipartisan Iraq Study Group, which outlined a plan last December for the withdrawal of most U.S. combat troops by early 2008.
Nine people were wounded in a rocket attack Tuesday, and four Asian contractors were killed in a barrage May 3.
State Department spokesman Tom Casey downplayed the latest attack, saying ``it's been part of the operating environment for our officials there, as well as for other people working there.''
``This is something, unfortunately, that has been a factor and a safety concern for our people since the beginning,'' he said. ``But certainly we are always looking at what we can do to better protect our staff and our facilities.''
Nevertheless, the recent increase in attacks has raised alarm among American staffers living and working in what had been considered an oasis of safety in the turbulent Iraqi capital. This month, the U.S. Embassy ordered diplomats to wear flak jackets and helmets while outdoors or in unprotected buildings.
Later this year, the United States plans to open a massive new embassy inside the Green Zone despite the ongoing security threat. Embassy staffers have expressed concern that the new facility lacks enough space to house the estimated 1,000 employees in safety.
Those concerns have risen because of a number of high-profile security breaches in the American-controlled zone, located on the west bank of the Tigris River, which flows through the center of the city.
In March, a rocket exploded near al-Maliki's office during a press conference for visiting U.N. Secretary-General Ban Ki-moon, who ducked behind the podium as the blast showered small bits of debris from the ceiling. Two Americans _ a soldier and a contractor _ died in that barrage.
A few days later, two suicide vests were found unexploded in the Green Zone, presumably smuggled in by someone with a security pass to enter the fortified area.
On April 12, a suicide bomber managed to penetrate the numerous security checkpoints, detonating an explosive belt in the cafeteria of the Iraqi parliament building. One Iraqi lawmaker was killed.
The latest attack on the Green Zone occurred as about 4,000 U.S. troops and 2,000 Iraqis continued to search for three U.S. soldiers feared captured by al-Qaida during an ambush last weekend in which four Americans and an Iraqi were killed.
Maj. Gen. Rick Lynch, commander of U.S. troops south of Baghdad, said the U.S. was offering rewards of up to $200,000 for information on the missing soldiers' whereabouts.
``We've done so much as to drain canals after a report that the bodies were in a canal,'' Lynch told The Associated Press. ``So we're leaving no stone unturned.''
Lynch said he was optimistic that the three soldiers would be found alive, and the search remained focused on the area where they went missing.
An al-Qaida front group, the Islamic State of Iraq, has said it captured the soldiers and warned the Americans in a Web statement on Monday to call off the hunt ``if you want their safety.''
At least 88 violent deaths were reported by police across Iraq on Wednesday, including 32 people who died the night before when a car bomb exploded near a market in the Shiite enclave of Abu Saydah northeast of Baghdad.
Hospital officials and victims said chlorine gas may have been used in the attack, but the U.S. military said it was still investigating whether the chemical was used as some of the victims experienced difficulties breathing.
Clashes also broke out in the mostly Shiite city of Nasiriyah in southern Iraq, when Shiite militants loyal to anti-U.S. cleric Muqtada al-Sadr battled police to protest the arrests of two of their members, police said.
Eleven Iraqis were killed and 75 wounded, police said.