BAGHDAD, Iraq (CNN) -- A man in an Iraqi army uniform opened fire on U.S. troops in Nineveh province Wednesday, killing two soldiers and wounding six others, a U.S. military spokesman said.
The six soldiers were in stable condition as of Wednesday night, the U.S. military said.
The U.S. military has not confirmed the identity of the shooter, but initial reports indicate that he was an Iraqi soldier, the military said in a statement.
The gunman, identified as Barazan Mohammed of Mosul, was killed in the ensuing exchange of fire.
An Interior Ministry official said an Iraqi soldier in a joint U.S.-Iraqi patrol opened fire on a group of U.S. soldiers in the same convoy after one of the American troops slapped an Iraqi soldier.
But the U.S. military disputed that, saying in a statement, "there was no altercation between the U.S. soldier and the Iraqi soldier."
The U.S. soldiers were in a courtyard waiting for their leaders to come out of a meeting when an Iraqi soldier entered the courtyard "and directly shot two soldiers, killing one, mortally wounding another, and then spraying the others before he was engaged by [coalition forces] counter fire and killed," according to a statement from a Multi-National Division-North spokesman.
"The U.S. soldiers had no conversation with this soldier and there was no interaction of any kind before they were murdered."
The Iraqi soldier was the only one wounded in the counterattack, the military said. The incident remained under investigation by the Iraqi and U.S. militaries.
The shooting occurred in the al-Zanjili area of Mosul, about 261 miles (420 kilometers) north of Baghdad, the ministry official said. The incident occurred about 5:30 p.m., officials said.
The ministry official said four U.S. soldiers were killed and three were wounded.
Earlier Wednesday, a car bomb exploded near an Iraqi police patrol in central Baghdad, killing four people and wounding 14 others, an Interior Ministry official said.
The attack took place in Naser Square about 9:40 a.m.
A roadside bomb also exploded near a car in a Shiite section of northeastern Baghdad, wounding seven civilians.
A car bomb also exploded in al-Shaab neighborhood of northeastern Baghdad, killing two people and wounding 10, an Interior Ministry official said.
Wednesday's violence came as the United Nations' top envoy in Iraq expressed "shock and outrage" over the killings of two Christian sisters in Mosul, the latest in a spate of anti-Christian violence there.
"This cowardly attack came hours after the U.N. High Commissioner for Refugees reported that some recently displaced Christian families are beginning to return to Mosul as the security situation in the city shows signs of improvement," according to a statement from envoy Staffan de Mistura.
More than half of Mosul's Christian population fled the city after a campaign of killings and intimidation, the U.N. said. The violence had tapered off in recent weeks, after 14 Iraqi Christians were killed in the city last month.
According to a Mosul police official, gunmen stormed a Christian family's house on Wednesday morning, killing two sisters and wounding their mother.
When police arrived to investigate, a bomb detonated outside the home's main entrance and wounded three officers, the official said.
CNN's Arwa Damon, Tommy Evans and Mohammed Tawfeeq contributed to this report.