Washington (CNN) US intelligence agencies and the Pentagon in recent weeks have tracked the movement of a number of Iranian short-range ballistic missiles into Iraq, a US official with direct knowledge of the situation said.

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.

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