A US embassy spokesman said a diplomat, whom he declined to identify, was in the area but was unaffected. He said Monday's attack appeared to be unrelated to the official's movements, but declined to give further details.
A spokesman for the Iraqi Islamic Party, a major Sunni Muslim grouping, said a senior US official had just left its compound in western Baghdad when his convoy was hit by an explosion which shattered windows in the party's headquarters.
Reuters journalists said US soldiers cordoned off the area after the blast, arriving in unusually large numbers for what was otherwise a fairly routine incident in Baghdad.
Aljazeera reported quoting Iraqi journalist Walid Khalid that the explosion occurred in Yarmuk district in central Baghdad, which has seen similar attacks before.
A US security helicopter that was flying over the convoy when the blast struck the area, evacuated what appeared to be three seriously injured American soldiers from the site.
Khalid told Aljazeera the bombing killed two Iraqi civilians and wounded eight others, five of them seriously.
Iraqi soldiers wounded in Baghdad
were taken to Yarmouk hospital
The explosion severely damaged nearby houses, shops, the municipal council building and al-Mamun police centre, he added.
Earlier on Monday, two car bombers targeted US and Iraqi security forces in separate attacks, killing at least 10 people and wounding more than 20, the Interior Ministry and police said.
The first blast occurred in Tikrit, near Saddam Hussein's hometown, where police pursued a suspicious driver who blew up his car after being cornered.
The blast killed two police officers and a firefighter and wounded 11 people, including seven civilians, the Interior Ministry said.
A second bomber blew up a vehicle near a joint Iraqi army and police patrol in the nearby city of Samarra, killing five members of the security forces and wounding five others, Iraqi police Major Salah al-Samarai said.
The injured were transferred to Samarra general hospital, Aljazeera learned.
The blast rocked eastern Samarra's al-Khadra neighbourhood at about 9am (0500 GMT) as an American-Iraqi patrol was passing by, police Lieutenant Qasim Muhammad said.
US soldiers secure the area after
Monday's attack on a convoy
The US military had no immediate details about the attack in Samarra, 95km north of Baghdad.
There has been a surge in car bombings in Iraq over the past six weeks, since a new government was formed, with many of them targeting Iraqi police and soldiers.
About 900 people have been killed in that time, most of them civilians.
In northern Iraq, a Kurdish human-rights activist was abducted by armed men in the northern Iraqi city of Kirkuk, an official from the Kurdistan Democratic Party said on Monday.
"Kurdish official and human-rights activist Shiman Ahmad Kader was kidnapped by unknown men in a northern district of Kirkuk [on Sunday]," said Najat Hassan Karim.
Craters caused by explosives now
pockmark many Baghdad streets
"We don't know where she is, but we accuse the enemies of Iraq and the Kurds, those who want to foment sectarian divisions, of being behind the abduction."
Kirkuk, an oil hub some 255km north of Baghdad, is an ethnic hotspot with its population of Kurds, Arabs and Turkmen.
Police in southern Iraq said on Monday they had arrested a member of Ansar al-Sunna, who confessed to a number of killings and kidnappings.
Baghdad resident Elias Khodr Mitaab Akkash, 31, was arrested outside the southern Iraqi city of Basra on Friday and reportedly confessed to shooting dead 14 people during elections in January as well as nine security men in other attacks.
"He confessed to having committed numerous killings and kidnappings in different places in Baghdad with a gang of 16 people," said a police spokesman.
Akkash reportedly also admitted to having kidnapped, raped and murdered two female students in the capital.