Islamic militants have posted graphic images online of alleged mass executions, claiming they have killed 1,700 Iraqi government soldiers.

Insurgents from the Islamic State of Iraq and Syria, who captured two major cities in northern Iraq last week, posted photos of soldiers in civilian clothing being loaded onto flatbed trucks, transported to an open field, and then their apparently lifeless corpses lying in a ditch.

When ISIS leader Abu Bakr al-Baghdadi left a U.S. detention camp in 2009, he gave a chilling farewell to reservists.

“He said, ‘I’ll see you guys in New York,’” Army Col. Kenneth King told the Daily Beast.

King said he did not take the utterance as a threat until five years later when he learned al-Baghdadi is the leader of ISIS.

“We spent how many missions and how many soldiers were put at risk when we caught this guy and we just released him,” said a frustrated King.

The ISIS photographs were posted on the jihadist website Welayat Salahuddin, according to the Associated Press. Iraq's top military spokesman, Lt. Gen. Qassim al-Moussawi, confirmed their authenticity and said he was aware of the mass murder of Iraqi soldiers, the Washington Post reported.

The New York Times said it could not confirm the authenticity of the photos. If they are real, this massacre would surpass the Syrian chemical weapons attacks, which killed 1,400 in Damascus.

Sources: Daily Beast, Washington Post