Rocket-propelled grenades were fired at the patrol in the Yussufiyah area, 20 km south of Baghdad, according to local residents.
Earlier, eyewitnesses told Aljazeera's correspondent that unknown assailants threw hand grenades at an American military patrol in the al-Amiriyah neighbourhood of the capital, killing two US soldiers.
A vehicle carrying Iraqi electricity company employees was also hit, killing one man and injuring a second.
A US military spokesman confirmed an attack had occured but declined to comment on the number of casualties. US soldiers were however quoted as confirming that at least one soldier was killed.
It was the latest in a spate of resistance attacks which have targetted occupation troops, two days after six British soldiers died and eight others were wounded in the southern town of al-Majjar al-Kabir after intrusive searches of local homes.
US troops also opened fire on a funeral procession in the capital, injuring three civilians, according to local residents.
Occupation troops arrived at the funeral when they heard gunshots being fired. Mourners tried to explain that this is a tradition but forces opened fire towards the house where the procession was beginning, said residents.
Since US President George W Bush declared an end to hostilities in Iraq on 1 May, at least 55 US soldiers have died in resistance attacks.
US Central Command said on Thursday one US Marine was killed and five others injured following a separate attack on a convoy in central Iraq on Wednesday.
The latest incidents coincide with statements from United Nations Secretary General Kofi Annan saying the world body does not currently have the capacity to take over security in occupied Iraq.
Annan was speaking after talks in London with Britain’s Prime Minister Tony Blair.
“Until the (UN Security) Council gives us a new mandate, we are not really talking of a UN force and, quite frankly, I doubt that we will have the capacity to take over that responsibility at this stage,” said Annan.
The world body did not endorse the US-led war against Iraq, launched on 20 March.
Occupation drags on
Meanwhile, a US senator who returned from Iraq said on Wednesday it was inaccurate to say the war was over.
War is far from over
Senate Foreign Relations Chairman Richard Lugar of Indiana said American troops would likely be bogged down in the oil-rich country for at least five years.
The Republican lawmaker said it was "rubbish" that US troops would be in Iraq for just as long as they were needed.
He called on the Bush administration to level with the American people.
Democratic Senator Joseph Biden, who was also in Baghdad with Lugar, said the White House's preparations for the occupation were insufficient.
"There's a gigantic gap between expectations and reality in terms of what the administration, in my view, anticipated," said Biden.
Biden described US Defence Secretary Donald Rumsfeld's expectation to scale-down US forces to 30,000 by the end of the year as "absolute fantasy".
Large costs expected
The two senators said US taxpayers should expect to be presented the bill for the war and occupation.
While the US occupation costs about $3 billion each month, the two senators said Iraq's oil revenues are expected to total $5 billion this year and $15 billion next year.
Meanwhile, there was a blast and fire at an oil pipeline feeding a key refinery early on Thursday in Fatha near Baiji, about 250 km north of Baghdad.
The Director General of Iraq's Northern Oil Company Adel al-Kazaz described the blast, the sixth in the country in two weeks, as "an act of sabotage".
Iraqi officials said they would step up police guarding the country's pipelines, an estimated 7,000 km, from 3,000 to 6,000. But US military officials say the task will be difficult.