US officials have previously said that Iran is fanning the violence in Iraq by giving sophisticated bomb-making technology, money and training to Shia groups who are attacking US and British troops.
Tehran has denied the charges.
In Baghdad, journalists were shown fragments of what the US official said were Iranian-made weapons, including one part of a penetrator and tail fins from 81-mm and 60-mm mortar bombs.
The official said: "The weapons had characteristics unique to being manufactured in Iran ... Iran is the only country in the region that produces these weapons."
Iran's foreign ministry, meanwhile, has claimed that the US, through its supervision of Iraq's defence ministry, is complicit in the kidnapping of an Iranian diplomat in Baghdad last week.
The Iranian embassy in the capital was trying on Sunday to obtain the release of the senior diplomat, but provided no news on whether they were close to succeeding.
|"The weapons had characteristics unique to being manufactured in Iran ... Iran is the only country in the region that produces these weapons"|
US defence official
The embassy official said "We have nothing new" and the office of the Iraqi prime minister said they could provide no more information since the announcement on Wednesday that four Iraqi military officers had been detained in connection with the affair.
Jalal Sharafi, 40, the second secretary at the Iranian embassy in Baghdad, was abducted in Karrada, a predominantly Shia southeastern district of the capital, on February 4 by men dressed in Iraqi army uniforms.
Another helicopter crash?
Also on Sunday, the US military said it had no knowledge of an American military helicopter crashing north of Baghdad.
Local residents in the area had earlier reported that one had crashed after coming under fire.
Lieutenant-Colonel Josslyn Aberle, a US military spokeswoman said: "We have no reports of a US military helicopter being down."
Residents reported seeing a missile hit an Apache attack helicopter, bringing it down in the Timayma area, near Taji, site of a major US air base 20km north of Baghdad.
Six helicopters have come down in Iraq in the last three weeks. The US military has confirmed that at least four of those were shot down after being struck by ground fire and says it has adjusted its tactics accordingly.