From ABC News:
U.S. officials say they have found smoking-gun evidence of Iranian support for terrorists in Iraq: brand-new weapons fresh from Iranian factories. According to a senior defense official, coalition forces have recently seized Iranian-made weapons and munitions that bear manufacturing dates in 2006.
This suggests, say the sources, that the material is going directly from Iranian factories to Shia militias, rather than taking a roundabout path through the black market. “There is no way this could be done without (Iranian) government approval,” says a senior official.