Two US soldiers and a senior Iraqi policeman have been killed in the northern city of Mosul.
Witnesses said the two American soldiers had their throats cut but this was denied by a US military spokesman, who said they had been shot.
In a separate attack, a US soldier died in a roadside bombing near Baquba, north of Baghdad, US officials said.
The Iraqi Governing Council, meanwhile, appointed Iraq's first ambassador to the United States in 13 years.
The council named Rend Rahim Francke as its Iraq's top diplomat in Washington.
The United Nations severed diplomatic ties with Iraq after former leader Saddam Hussein invaded Kuwait in 1990.
Ms Rahim, a veteran Washington lobbyist, told reporters: "I want to build the embassy to be the face of Iraqi diplomacy... and the new democratic and civilised Iraq."
The two US soldiers were killed in the centre of Mosul after the attackers approached their vehicle in traffic and slit their throats, witnesses said.
But a military spokesman said: "Two soldiers from the 101st Airborne Division were killed shortly after midday in west Mosul ...they were shot while en route from one compound to another."
Francke is Iraq's first US ambassador for 13 years
The witnesses said that US troops immediately surrounded the vehicle and began interrogating Iraqis in the area.
The latest attacks brought to 185 the number of US soldiers killed in action since President George W Bush declared major combat operations in Iraq over on 1 May.
Elsewhere in Mosul, Iraqi police said a top police officer was killed by unknown gunmen in a car late on Saturday.
Colonel Abdel Salam Qanbar - who was in charge of oil installations in the area - was gunned down as he "was leaving the mosque" in the evening, Iraqi police general Khaled Fathi Jassim told the AFP news agency.
In the Baquba attack, the US soldier from the 4th Infantry Division was killed and two others wounded when their convoy hit an "improvised explosive device," a US military spokesman said.
The spokesman, Lieutenant Colonel Bill MacDonald said that the incident happened at about 0740 local time (0440 GMT).
The attack came only a day after car bomb rocked the city's main police station, killing seven policemen and two civilians, a US military spokesman said.