In an interview with Iraqiya TV, Iraqi Prime Minister Haider al-Abadi said that ISIS took control of thousands of US imported Humvees when it captured Mosul on June 10, 2014.
The vehicles captured by ISIS in Mosul would be worth more than $1 billion in total if sold.
The stolen Humvees were part of the large amount of hardware the US left behind in Iraq after US forces began pulling out in 2009.
ISIS has captured more equipment from the Iraqi army in other battles where their fighters push for more control in Anbar province.
One of the stolen US humvees was used in a suicide bombing at an army base near Baghdad that killed at least 45 people. The attack involved three explosives-laden car bombs escorted by one of the stolen Humvees, according to the BBC.
"In the collapse of Mosul, we lost a lot of weapons, we lost 2,300 Humvees in Mosul alone," Abadi said an interview Sunday.
Late last year, the US State Department approved a deal to sell Iraq 175 M1A1 Abrams tanks, worth $12.4 billion, and 1,000 military Humvees, valued at $579 million.
Congress has yet to approve the sale, and some lawmakers have expressed concern that the US sending arms to Iraq may eventually lead to ISIS acquiring the equipment again.
ISIS generally rely on civilian vehicles and pickups like the Toyota’s Hilux and Land Cruiser trucks. The stolen Humvees are much sturdier and can be used as lead vehicles in attacks.