The deaths of more civilians come as Iraqis begin reassessing the controversial role of the US military in their war-ravaged country.
Iraqi security officials said three women and a man were killed when the minibus in which they were travelling came under American military fire in Baghdad's northeastern Al-Shaab neighbourhood.
The vehicle was carrying employees of Al-Rasheed bank and the gunfire wounded another two people -- a woman and a man, they said.
A US military spokesman told AFP US forces fired on a minibus in Baghdad "after the driver failed to heed a warning shot".
"The bus was travelling on a street that is off-limits to vehicles other than passenger cars," the spokesman said.
"Initial reporting indicates that two passengers were killed and four wounded. The incident is under investigation."
In a separate statement the military said its troops opened fire on a car which tried to speed through a roadblock during an operation against Al-Qaeda in Iraq on Monday, killing a child and two men.
Two men in a vehicle sped towards the checkpoint and ignored warnings to stop while troops were conducting the operation in Baiji some 200 kilometres (140 miles) north of Baghdad, the statement said.
"The ground force fired warning shots, but the driver attempted to speed through the roadblock. Perceiving hostile intent, the ground force engaged, killing both men," the statement said.
A wounded child was found inside the vehicle and was transferred to a military medical facility where he died, it said.
"We regret that civilians are hurt or killed while coalition forces work diligently to rid this country of the terrorist networks that threaten the security of Iraq and our forces," said US military spokesman Commander Ed Buclatin.
According to the Iraqi Body Count website, which keeps an independent tally of Iraqi deaths, between 77,333 and 84,250 civilians have been killed since the US-led invasion of 2003.
US President George W. Bush and Iraqi Prime Minister Nuri Al-Maliki agreed on Monday that they would begin negotiations early next year on the terms of an American military presence in the country beyond 2008, officials said.
The two leaders signed a non-binding statement of principles for the talks, setting a July 31, 2008 target date to formalise US-Iraq economic, political, and security relations.
Maliki announced in Baghdad on Monday that the accord sets 2008 as the final year for US-led forces to operate in Iraq under a United Nations mandate, which will be replaced by the new bilateral arrangement with Washington.
Iraqis on Tuesday blasted Maliki for signing the pact.
The hardline Sunni religious body, the Muslim Scholars Association, said the agreement gave the US a right to "kill, demolish and humiliate Iraqis."
"This will provoke our people who will look at those who signed as collaborators with the occupier," said the association, which is allegedly linked to several anti-American Sunni insurgent groups.
Sunni lawmaker Dhafir al-Ani said the agreement gives "the US a chance to interfere in different aspects of (Iraqi) life."
Liwa Sumaysim, MP from the political group of anti-American Shiite cleric Moqtada al-Sadr, insisted that Maliki stick to his pledge that parliament have the final say on any deal reached with the US.
"We have strong reservations on the pact, although it is a non-binding one. The Iraqi parliament must have the final word on it," he said.
Meanwhile, 13 people were killed on Tuesday in a spate of attacks north of Baghdad, security officials said.
A suicide bomber detonated his explosives-filled vest in front of police headquarters in the central city of Baquba, killing seven people, police said.
Two people were killed in mortar attacks on homes in Buhriz, south of Baquba, while one person was killed when a civilian car was hit by a roadside bomb in Dali Abbas, 40 kilometres (25 miles) northeast of Baquba.
In Tikrit, a civilian was shot dead in the city centre by unknown gunmen, while a policeman was killed when insurgents opened fire on a police patrol at Al-Hawijah, 50 kilometres (30 miles) west of Kirkuk.
A leader of the Ambagiyah tribe was shot dead by insurgents in the village of Ambagiya, 20 kilometres (12 miles) north of Baquba.
© 2007 Agence France Presse