Thunderous explosions about 7:45 p.m. local time (11:45 a.m. ET) rocked the area around the two-mile square "green zone," which includes coalition headquarters, the military press center and other key facilities.
It's believed the weapon used was an 81 mm mortar launcher with a range of four miles, reports CBS News Correspondent David Hawkins.
At the Pentagon, spokesman Lt. Col. Jim Cassella said four people had been injured in the attacks. He said it was not immediately clear whether the victims were military or civilian personnel or whether they were Americans.
Cassella said there appeared to have been three explosions, possibly from mortars or rockets. Three of the injured were taken to a hospital and one was treated at the scene, Cassella said.
It was the second mortar attack on the capital in as many days. On Monday night, five mortar shells fell on central Baghdad, harming no one. Amid the continuing violence, key U.S. ally Spain pulled many of its diplomats out of the city.
In other developments:
The blasts came at the end of a day that saw an apparent weakening in foreign support for the U.S. led mission in Iraq.
Spain said it was withdrawing much of its diplomatic staff from Iraq for security reasons, the third coalition country to do so in the past two weeks amid mounting violence. The Turkish ambassador to the United States says his country won't send peacekeeping troops into Iraq without an invitation from the U.S.-picked Iraqi Governing Council.
Russian president Vladimir Putin says his country won't lend troops to an international peacekeeping force in Iraq. And a group of Thai senators urged their government to withdraw its troops from Iraq.
Bush administration officials have made a priority since the war began of enlisting foreign help. Tuesday's announcements could be a setback for that effort.
The Spanish Embassy will remain open but with minimal staffing and a significant number of its 29-member staff is being pulled out, a Foreign Ministry official said.
"We have taken staff out of Baghdad temporarily given that it is a very complicated moment," Spanish Foreign Minister Ana Palacio was quoted as saying by the Spanish news agency Europa Press. She did not say exactly how many diplomats were being withdrawn.
In late October, Bulgaria and the Netherlands moved Embassy staff in Iraq to Jordan, both citing safety concerns following a attacks on diplomatic and humanitarian agencies — including deadly bombings at the Turkish Embassy and the U.N. headquarters.
The Red Cross, United Nations and Doctors Without Borders reduced staff levels in last week.
Meanwhile, Iraq's interim authority is calling on the U.S. to give Iraqis a greater role in the defense of their country.
The Iraqi Governing Council says Iraqis are better able than Americans to combat the resistance. The council says it would like to see the U.S. transfer more power, especially in security affairs.
The dramatic increase in American hostile fire deaths this month was due to Sunday's downing of a CH-47 Chinook helicopter, which was carrying dozens of American soldiers on leave. Casaulty figures were confused Tuesday, but somewhere beteen 16 and 21 Americans died and another 20 were wounded.
The recent, bold attacks represent a major escalation in the campaign by a shadowy group of insurgents fighting to drive occupation forces out of Iraq. They also illustrated the vulnerability of American lines of communication to guerrilla ambushes and roadside bombings.
"The enemy in Iraq believes America will run, that's why they're willing to kill innocent civilians, relief workers, coalition troops," Mr. Bush told an audience in Birmingham, Ala. on Monday. "America will never run. America will do what is necessary to make our country more secure."
Until now, the U.S. military has believed that helicopters and transport planes provided a relatively safe mode of transport for ferrying troops and supplies around the country. That has been called into question by Sunday's attack on the Chinook.
Hundreds of SA-7 Strelas from the prewar Iraqi army are believed to have ended up in guerrilla hands along with a number of the advanced SA-18 Iglas equipped with special filters to defeat flares and other countermeasures deployed by U.S. aircraft.
The Chinook attack was the largest U.S. death toll in any single action since the invasion of Iraq began March 20.