The Pentagon is investigating whether a recent attack on a military compound in Karbala was carried out by Iranians or Iranian-trained operatives, two officials from separate U.S. government agencies said.
"People are looking at it seriously," one of the officials said.
That official added the Iranian connection was a leading theory in the investigation into the January 20 attack that killed five soldiers.
The second official said: "We believe it's possible the executors of the attack were Iranian or Iranian-trained."
Five U.S. soldiers were abducted and killed in the sophisticated attack by men wearing U.S.-style uniforms, according to U.S. military reports.
Both officials stressed the Iranian-involvement theory is a preliminary view, and there is no final conclusion. They agreed this possibility is being looked at because of the sophistication of the attack and the level of coordination.
"This was beyond what we have seen militias or foreign fighters do," the second official said.
The investigation has led some officials to conclude the attack was an "inside job" -- that people inside the compound helped the attackers enter unstopped.