Islamic State (IS) militants may have captured as many as 2,300 US-provided armored Humvees from Iraqi armed forces when they seized Mosul in 2014, Prime Minister Haider al-Abadi admitted on Sunday.

"In the collapse of Mosul, we lost a lot of weapons... We lost 2,300 Humvees in Mosul alone," Abadi said in an interview broadcast by state run Al Iraqiya television, according to remarks carried by AFP.

IS overran Mosul, Iraq's second city, in June 2014, routing a far larger force of 30,000 Iraqi soldiers who retreated in disarray, stripping out of their uniforms and abandoning their equipment as they fled.

The jihadists took control large stores of weapons, munitions, and vehicles. In the days afterwards, Humvees with hurriedly painted over Iraqi markings and carrying IS's black flag were visible from frontline positions held by Iraqi Kurdish peshmerga fighters. IS has since made extensive combat use of them, including as vehicle-borne improvised explosive devices.

On Monday, a Humvee was used in an IS suicide bombing on a military base north of Fallujah that killed 42, a military source told Al Jazeera.

The value of the lost vehicles is unknown. But in December 2014, the US State Department approved a possible sale of 1,000 Humvees armed with machine guns, and grenade launchers to Iraq at an estimated cost of $579 million.

With the help of airstrikes carried out by an American-led coalition and international backing, pro-government forces had been slowly regaining territory, including taking control of Saddam Hussein's birthplace of Tikrit.

IS seized Ramadi, the capital of Anbar province last month, however, in an embarrassing defeat for Baghdad and Washington's anti-IS strategy.