The Iraqi military's chief of staff, Lieutenant General Babaker Zebari, "estimated that it will take several more years before Iraq can provide for its external defence without assistance from international partners," said the report from the US Special Inspector General for Iraq Reconstruction (SIGIR).
"General Zebari suggested that the (Ministry of Defence) will be unable to execute the full spectrum of external-defence missions until sometime between 2020 and 2024, citing (Iraqi government) funding shortfalls as the main reason for the delay," the report said.
"Iraq will not be able to defend its own airspace until 2020, at the earliest," Zebari told SIGIR, adding that "an army without an air force is exposed."
Iraq has ordered 18 F-16 warplanes from the United States, but it will be years before that force is fully operational.
Zebari has stated before that his forces will require training for another decade before they are fully capable of securing the country.
Iraq's military has been tied down by years of bloody internal conflict here, with US officers saying it needs to transition to a more traditional role of external defence.
US President Barack Obama announced on October 21 that all US soldiers will depart the country by the end of 2011, after protracted and ultimately failed negotiations with Iraq about a post-2011 US military training mission here.
The roughly 39,000 US soldiers still in Iraq are now in the process of drawing down, after a nearly nine-year campaign that has left thousands of American soldiers and tens of thousands of Iraqi dead, with costs running into billions of dollars.