Russia supplied an initial delivery of the aircraft just a few days ago but analysts at the International Institute for Strategic Studies (IISS) here say that a further delivery on July 1, originates from Iran, BBC reported.
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 (ISIS).
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 (IRGC).
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.
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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