While some of the missiles may be categorized as ballistic, the official emphasized that they are very short range, without offering more details.
The concern is the missiles could now be moved into areas where they could be fired at US troops by Iranian-backed militias. Senior US military officials, however, have said recently that they don't believe the regime in Tehran is likely to go to war against the US.
In a related development, the official said that in the last month these militias have stepped up attacks against US positions with larger rockets than had been seen before.
The New York Times was first to report the movement of missiles into Iraq.
News of the movement of Iranian missiles into Iraq comes a day after CNN reported there is fresh intelligence of a potential Iranian threat against US forces and interests in the Middle East, according to several US defense and administration officials.
"There has been consistent intelligence in the last several weeks," one administration official told CNN. A second official described it as information that has been gathered throughout November. The information is being gathered by military and intelligence agencies.
The officials would not say in what format the intelligence exists. But in the last several weeks there has been movement of Iranian forces and weapons that the US worries could be put in place for a potential attack, if one is ordered by the Iranian regime, the officials said. It's not clear if a potential threat would come from the central government or Iran's Islamic Revolutionary Guard Corps.
The head of US military operations in the Middle East recently signaled the US expects some kind of Iranian action in response to the US sanctions and pressure campaign that is trying to get the regime to abandon its nuclear program.
"I would expect that if we look at the past three or four months, it's possible they will do something that is irresponsible. It's possible that they'll lash out at their neighbors," Gen. Kenneth McKenzie, head of the US Central Command, told an audience in Bahrain at the time. "It is not going to be productive for them in the long term to choose to act out in the military domain. That's the message that we're trying to convey."
Officials were adamant the intelligence has been gathered solely as part of the continuous monitoring by the US and has nothing to do with President Donald Trump's political concerns over the impeachment inquiry.
The intelligence has moved through professional military and intelligence channels, and it is not clear whether Trump has yet been briefed on it in detail.