Feels like defeat: US air force bombs US-made army kit to foil Islamic State

The grainy black-and-white footage shows a military vehicle, a small dark mass in the crosshairs of a United States war plane, seconds before it explodes in a flash of light.

That August 16 strike in northern Iraq, shown in video released by the US military, killed an unknown number of Islamic State fighters - and destroyed one US-made armoured vehicle that had cost up to US$300,000.

Since the Obama administration began strikes there on August 8, US fighter jets and drones have destroyed Iraqi military vehicles provided by the US - worth an estimated US$3 million to US$4 million but which were later seized by Islamists who now control a third of Iraq.

The growing tally of US-made, US-destroyed weaponry shows how far Iraq has veered off the course the Obama administration had expected when American forces withdrew in 2011.

US officials had hoped their efforts to train and arm the Iraq military, at a cost more of than US$20 billion, would guarantee stability. "When you see your own equipment blown up by US airplanes, there's this inherent feeling of defeat, even if it doesn't have an American flag on it any more," says Matthew Pelak, a former US infantry sergeant sent to Iraq in 2004, who now works as a fireman in New York. "It's incredibly discouraging."

When Iraqi soldiers abandoned bases in large numbers ahead of Islamic State's advance across northern Iraq in June, they left behind guns and sophisticated fighting weaponry.