The latest deadly attack, which on Monday took to 104 the number of US soldiers killed in Iraq since major hostilities were declared over on 1 May.
It followed messages attributed to America's fugitive foes Saddam Hussein and Usama bin Ladin. US President George Bush, meanwhile, said the messages would only strengthen his resolve to fight "terrorism".
A US soldier was killed and five were wounded in an attack in the flashpoint town of Falluja, a statement said.
"At 1pm (10:00 GMT) today in Falluja, a patrol from the 82nd Airborne Division was attacked," it said. The attack involved an explosive device "followed by small arms fire."
The attack was at least the third in the hotspot town in two days in the wake of messages, purportedly from ousted Iraqi leader Saddam and al-Qaida chief bin Ladin, issuing calls to arms against the US-led occupiers.
Call for funds
US officials, meanwhile, stepped up their attempt to secure more funds for rebuilding Iraq before the two-day donors conference which opens in Spain on Thursday.
"I hope they will come in a generous manner to help the people of Iraq"
US secretary of state
"I hope they will come in a generous manner to help the people of Iraq, to make a statement to the Iraqi people that the international community is there with them and for them," Secretary of State Colin Powell told business leaders on the sidelines of the annual Asia-Pacific Economic Cooperation (APEC) forum.
"(I hope) that the international community will come together not only to give them funds, but to give them hope, hope for a better future," he said.
In an attempt to overcome resistance to providing large cash and in-kind donations, Washington has endorsed two key provisions, giving non-US players a say in how reconstruction funds are spent, officials said.
Both provisions are to be discussed in Madrid, where organisers hope to meet as far as possible the need for what a World Bank and UN report has estimated as $36 billion in reconstruction aid between 2004 and 2007.
Major investment absent
And as donor countries prepared to gather in Madrid, Iraq was counting on the international community to provide the funds to repair its blighted infrastructure.
"There has been emergency and maintenance work done on the infrastructure," said Nada Doumani, a Red Cross spokesperson in Baghdad.
"But until now there hasn't been any major investment... I think the Coalition Provisional Authority is very much aware of the need to invest in everything."
Japan has pledged $1.5 billion for next year, but the US requests for aid have met with an icy response from France, Germany and Russia.
The US Congress has approved Bush's request for $20.3 billion in civilian reconstruction funds.