A US military spokeswoman said the blast hit a Bradley armoured vehicle in the northwestern sector of the capital on Thursday.
None of the soldiers in the vehicle survived the blast, Captain Patricia Brewer said.
The US casualties came on a day when 18 Iraqi workers were found dead in Mosul after they were lured to the northern city by promises of well-paid work at US bases.
However, the governor of Nainawa province denied the report. "We have not heard about such an incident in Mosul city," Nainawa governor Duraid Kashmula told Aljazeera on Thursday.
Mosul is the capital of Nainawa governorate.
The victims, aged between 16 and 42, were apparently driven by poverty in their village of Bayda in the relatively peaceful southern province of Zi Qar to seek work in Baghdad from where a mysterious contractor lured them north.
"The contractor did not accompany the workers but gave them an address in northern Iraq and told them to go there," said Naim Husain Farhan Khafaji, whose brother was one of the 18.
Distraught relatives of the men, who were almost all related, gathered at a Baghdad hospital on Thursday to collect their bodies, which had all been found with a bullet to the head.
In other violent incidents, Aljazeera has learned, unidentified assailants on Thursday killed the chief of police in Sadr City, east of Baghdad.
Neighbours have called for a
massive turnout for the elections
While in Abu Ghraib, west of Baghdad, armed men assassinated Muhammad Musa al-Janabi, a key member of interim Prime Minister Iyad Allawi's party, the Iraqi National Accord.
And in Samarra, two members of the Iraqi National Guard were killed and another three wounded in clashes with armed men.
Meanwhile, in the northern town of Shirqaat, south of Mosul, unidentified armed men dynamited an electoral centre.
In the same town, Aljazeera quoted a medical source as saying that an Iraqi contractor working for US forces was killed by armed men.
Also, two other Iraqis who were securing traffic for a US patrol were shot dead by US forces.
A group of armed men freed Shirqaat's commissioner after having taken him captive several days ago.In Baghdad, a leader of the Iraqi Communist Party, Hadi Salih, was found strangled to death, his eyes blindfolded and hands tied with metal wire.
Huge turnout urged
Against this backdrop of continued violence, foreign ministers and diplomats from Iraq' neighbouring countries met on Thursday in the Jordanian capital Amman to discuss the Iraqi elections scheduled for 30 January.
"A lot has been achieved and all issues are being resolved according to the agenda. But in the final analysis, Iraqis are the only decision makers of the electoral process"
UN spokesman on Iraq
At the meeting, ministers from Syria, Jordan, Saudi Arabia, Kuwait, Iran and Turkey called for a massive turnout in the Iraqi elections.
Yusif al-Sharif, Aljazeera's correspondent accompanying the Turkish team, reported that most nations, including Syria and Iran, sent high-level delegations, but Iranian Foreign Minister Kamal Kharrazi was absent.
The delegates produced a clear and unified message urging all Iraqi factions, especially Sunnis, to participate in the 30 January election.
The final statement was an acknowledgment by Iraq's neighbours of their responsibility to ensure that all Iraqi groups took part in the election and to abstain from interference in Iraq's internal affairs.
The 12-point communique, which was agreed upon by the various ministers in attendance, underscored the Arab identity of Iraq and cautioned against outside efforts to influence the election's outcome.
Some diplomats said Thursday's meeting in Amman was among the least contentious gatherings of Iraq's neighbours so far, going by the unanimous agreement on the basic issues.
UN's role defended
Conference sources said the objections raised by the Syrian and Iranian delegations to the mention of "interference in Iraq's forthcoming election", were eventually taken care of.
Jordan has been at the helm of
efforts to boost stability in Iraq
Speaking to Aljazeera, Ayman al-Safadi, media spokesman of the United Nations in Iraq, said: "The UN backs all efforts aiming to achieve this target, as the welfare of nations all over the world lies in overcoming this difficult situation in Iraq and making clear and consistent progress in order to restore security and stability in the country."
He added: "The UN role in Iraq abides by the Security Council's Resolution 1546, which says its role should be to offer technical support and strategic advice to the Iraqi Independent Election Commission, which is responsible for carrying out, organising and assessing the elections.
"Technically, UN experts have cooperated with the Independent Election Commission for the elections in Iraq. A lot has been achieved and all issues are being resolved according to the agenda. But in the final analysis, Iraqis are the only decision-makers of the electoral process."