US-trained Iraqi units facing investigation over alleged ISIS-like atrocities

Iraqi officials are investigating a number of U.S.-trained Iraqi military units accused of committing atrocities against civilians, including ISIS-like beheadings.

U.S. State Department and Defense officials confirmed the investigation, first reported by ABC News, on Thursday. They said the Pentagon has been aware of the allegations for some time and it has already withheld funding and other assistance from units that have been tied to possible war crimes.

A Defense official told Fox News assistance for certain units was withheld “on the basis of credible information in the past.” The official was unable to go into detail about which units have been penalized, or what they had been accused of.

The report by ABC News, however, said a “trove of disturbing images” was discovered “circulating within the dark corners of Iraqi social media since last summer.” The report says the units and collaborating militias in these alleged crimes – which range from torture and extra-judicial executions, to human heads used as trophies and corpses dragged behind Humvees – were often called the “Dirty Brigades” among U.S. and Iraqi circles.

“Usually, when forces commit such crimes they try to hide them,” Sarah Leah Whitson, Middle East Executive Director at Human Rights Watch, told ABC News. “What we’re seeing here is brazen, proud display of these terrible crimes."

The U.S. poured some $25 billion into training Iraqi Army forces since the U.S. invasion and toppling of Saddam Hussein in 2003. Many of those forces are now fighting to extract ISIS fighters from key strongholds in Iraq, including the cities of Mosul and Tikrit.

But allegations of brutality and torture in these Shiite-led Iraqi government forces are not new, and can be traced back to the early days of the war. Before and after the American withdrawal of forces from the country in 2011, charges of anti-Sunni abuse in Iraqi prisons, for example, led to protests and a widespread Sunni backlash against the government. This later helped to fuel the growth of Al Qaeda in Iraq (AQI), which morphed into the Islamic State, or ISIS, which took advantage of the volatility and anger on the Sunni street.

More recently, ISIS has been the group beheading prisoners and carrying out atrocities against civilians and soldiers on the battlefield. It has drawn U.S. forces back into the region, including advisers on the ground and fighters conducting airstrikes.

Now the Iraqi government has been forced to look within at its own possible war crimes. Depending on how widespread the problem, it could cost the government a significant amount of American support. According to the so-called Leahy Law, first introduced in 1997, the Pentagon and U.S. State Department are prohibited from giving assistance to any foreign military units that violate human rights with impunity.

Vermont Democratic Sen. Patrick Leahy himself, the sponsor, after viewing the images provided by ABC News, said, “I would say this involves the Leahy Law … and I argue that we should be withholding money.”

State Department spokeswoman Jen Psaki said Thursday that the U.S. would not be engaging in its own investigation, however. “U.S. officials from Washington and Baghdad continue to raise our concerns with senior government of Iraqi officials and have been doing that for some time,” she said.

“Their behavior must be above reproach or they risk being painted with the same brush as ISIL fighters,” she added, “so that’s a message we are making clear.”

Fox News' Jennifer Griffin and Lucas Tomlinson contributed to this report.