Iran is secretly flying surveillance drones over Iraq and sending military equipment there to help Baghdad in its fight against Sunni insurgents, The New York Times has reported.
A "small fleet" of Ababil drones was deployed to the Al Rashid airfield near Baghdad, the newspaper reported on its website on Wednesday, citing anonymous US officials.
Tehran has also installed an intelligence unit at the airfield to intercept electronic communications between fighters and commanders with the Islamic State of Iraq and the Levant (ISIL, also known as Isis).
Ababil drones, less sophisticated than US unmanned aircraft, are designed in Iran and have a nearly three-metre wingspan. They are used for surveillance and are unarmed.
About a dozen officers of Iran's paramilitary Quds Force have also been sent to Iraq to advise commanders there and help mobilise Shiite militias in the south of the country, the paper reported.
Iran is also sending two flights daily to Baghdad with 70 tonnes each of military equipment and supplies.
"It's a substantial amount" of material, a US official told the newspaper. "It's not just light arms and ammunition." Tehran has massed 10 divisions of its army and its Quds Force troops along the border, ready to act if the Iraqi capital or Shiite shrines are threatened, The Times added.
Asked at a briefing, US State Department spokeswoman Marie Harf said she "can't confirm the specifics in those reports".
But she said "anyone in the region shouldn't do anything that might exacerbate sectarian divisions, that would fuel extremism inside Iraq".