This means that the US -- which has also sent aircraft to Iraq -- is operating alongside Iran in this conflict. The US has deployed drones and helicopters to Iraq and is actively gathering intelligence on the advance by the Islamic State in Iraq and the Levant.
The US is also supplying Iraq's existing air force with Hellfire missiles, the report said. Joseph Dempsey, an analyst for the IISS's Military Balance publication, has carefully studied video of the aircraft released by the Iraqi authorities.
He told the BBC that he believes that some of the aircraft -- Sukhoi Su-25 "Frogfoot" jets -- operating in Iraq are indeed Iranian. "Imagery analysis," he says, "makes this the most logical conclusion. The markings, serial numbers and camouflage all fit with what we know of the Iranian fleet."
Iran maintains a small number of Su-25 aircraft, operated by the Iranian Revolutionary Guard Corps. Ironically, the majority of these aircraft used to be part of the Iraqi Air Force -- seven Su-25s sought refuge in Iran during the First Gulf War.
Contrary to Iraqi wishes, these aircraft were retained and later brought into Iranian service. It is much harder to determine who is actually flying the aircraft, the report said.
Dempsey was quoted as saying that "while Iraq may retain some capability, having operated the aircraft in the past, any pilots would not have had any flying experience for at least 11 years. "So it would strongly suggest that some level of external support is required," he said.
Iraq's leadership is facing increased pressure to form a new government to deal with the Sunni militant onslaught that has threatened to tear the country apart.
The United States has deployed an additional 300 military personnel in Iraq to augment the security of American embassy in Baghdad, its support facilities and the Baghdad International Airport.
Iraq is witnessing serious strife with Sunni militants, backed by the al Qaeda, capturing two key cities and marching towards Baghdad. Hundreds of thousands of Iraqis have been displaced in about three weeks of fighting.
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