Top US Military Official Repeatedly Warned Iraq About Troops' Conduct

America's top military official, Chairman of the Joint Chiefs of Staff Martin Dempsey, repeatedly warned Iraqi leaders about the conduct of both the Iraqi military and the militias that fight alongside them, a senior U.S. official told ABC News.

The Iraqi government says it has launched an investigation into alleged atrocities committed by Iraqi troops and Shia militias, some captured in a trove of images and footage found online, as revealed in an ABC News investigation Wednesday. Today State Department spokesperson Jen Psaki said the images amounted to "disturbing and serious allegations."

"This behavior is clearly - you know - their behavior must be above reproach or they risk being painted with the same brush as ISIL [ISIS] fighters and certainly that's a message that we are making clear," Psaki told reporters today.

[A bound and blindfolded detainee appears to be dropped - or possibly hung from the neck according to one analyst -- from what looks like an Iraqi military base guard tower. The image was posted on Instagram.]

A senior military official with the Joint Staff disclosed to ABC News last week that "certain Iraqi units" had been denied military aid and assistance on the basis of "credible information in the past" -- the result of what's known as the Leahy Law, named for Sen. Patrick Leahy, D-Vermont, and designed to keep the U.S. from directly funding units who commit human rights abuses.

The U.S. has blocked aid to the un-named Iraqi units under the Leahy Law since American troops returned to Iraq in August and began supporting government forces and Kurdish Peshmerga fighters with airstrikes against ISIS jihadists, the senior official said.

ABC News first showed administration officials, as well as Leahy, dozens of examples of social media images posted by members of Iraqi Security Forces and their supporters last fall. Some administration officials downplayed it as not widespread or involving Baghdad's military, but Leahy was incensed.

"The Leahy Law is clear and sets a minimum standard. If there is credible information that foreign security forces have committed the worst crimes - such as torture, killings of civilians, rape, or executions of prisoners - then they are not eligible for U.S. aid unless the individuals involved are being appropriately punished," Sen. Leahy said this week.

Iraqi Army spokesperson, Gen. Saad Maan, told ABC News after viewing some of the images that were posted online that "of course" Iraq will investigate.

"We don't have anything to hide," the general said. "We don't have anything to be in, let's say, in a black corner."

[A black uniformed individual holds the severed head of a purported Saudi ISIS fighter while standing on top of a black-painted Humvee. In the background, a man wears two patches signifying the Iraqi Interior Ministry's Emergency Response Brigade.]