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Iraqi security forces fire artillery during clashes with Sunni militant group Islamic State of Iraq and Syria on the outskirts of the town of Udaim in Diyala province, June 22, 2014. Gunmen seized an Iraqi-Syrian border post in Iraq's western Anbar province on Sunday, security sources said, a day after Sunni militants fighting the Baghdad government grabbed another border crossing further north. REUTERS/Stringer

Pentagon officials say they are aware of pictures posted by the Islamic State of Iraq and Syria showing U.S. Humvees being shipped to al Qaeda rebel forces in Syria.

The Washington Free Beacon, an online newspaper from the Center for American Freedom, said the vehicles were captured from the Iraqi military along with tanks, trucks and arms, and are expected to give ISIS an advantage over other rebel groups.

“We’re aware of reports of some equipment -- namely Humvees -- and the pictures that have been posted online,” Pentagon spokesman Cmdr. Bill Speaks said in an e-mail to the Free Beacon. “We are certainly concerned about these reports and are consulting with the Iraqi government to obtain solid confirmation on what assets may have fallen into ISIL’s hands.”

Speaks said there are no firm numbers on captured arms and equipment. The weapons came from Iraq's Second Division, which included a motorized brigade and several infantry brigades. The division was based in Mosul, which fell to ISIS earlier this month.

Speaks denied, however, ISIS also had obtained Blackhawk helicopters, saying none ever had been sold to Iraq.

Militants Sunday seized two border crossings, one with Syria and one with Jordan, Iraqi military officials said. The Associated Press reported ISIS had seized the Turaibil crossing with Jordan and the al-Walid crossing with Syria following a pullout by government forces.