The attack on the 21-vehicle convoy happened at al-Rutba, a third of the way into Iraq from the Jordanian border, the official said.
There were no immediate details of any casualties, but several people were unaccounted for, he added.
The convoy, not escorted by US military vehicles, was operated by a sub-contractor of Kellogg, Brown and Root (KBR), itself a subsidiary of US energy and services giant Halliburton.
It was not clear if the sub-contractor was an Iraqi or a foreign company, said the official. The convoy was on a routine trip thought to be supplying a US-led occupation civilian or military base.
Nobody from KBR was immediately available for comment.
Last month, resistance fighters hit many civilian convoys including one in which Mississippi truck driver Thomas Hamill was captured and held hostage for three weeks before he escaped.
Meanwhile, Russia said on Tuesday one of its nationals had been killed and two others taken hostage in Baghdad, just a month after a similar incident prompted hundreds of former Soviet nationals to flee for home.
Russian foreign ministry spokesman Alexander Yakovenko said, "we are doing everything we can to free our citizens.
Russian nationals were advised by
their government to leave Iraq
"As the foreign ministry had repeatedly warned, the situation in Iraq is very difficult. We had earlier urged our citizens to leave Iraq and not to return until the situation is stabilised," he said in a statement.
But he also said Russia was still trying to find out the details of the incident and that no one had yet established contact with the hostage-takers.
Russian diplomats said the three were employed by the Interenergoservice company that was under contract to restore energy supplies to the war-torn country.
Not the first
A group of armed men attacked the Russians as they returned from work by car to Baghdad late on Monday afternoon. They were trying to rebuild an electric power plant located about 50km south of the Iraqi capital.
Russian officials said no one had yet claimed responsibility for the attack and that no ransom or other demands had been made for the hostages' release.
A group of Russian, Belarusian and Ukrainian workers were briefly taken hostage in Iraq last month.
One was released immediately and the others within 24 hours after the hostage takers learned that most of them were from Russia - a country that furiously opposed the US-led war on Iraq.
Russia's foreign ministry advised all Russian workers to pull out of Iraq after the April incident.
Also on Tuesday, the body of a westerner, believed to be American, was found in Baghdad, a senior US military official told reporters.
He said the westerner, whose body was found on Monday, was not a member of the US armed forces and did not work for the Defence Department, but would offer no further details.