CNN reports that about 50 members of the Abu Nimr, an important clan in Anbar province, were taken from their homes in the middle of the night and then publicly executed. They became the latest members of the tribe to suffer at the hands of Islamic State.

The abduction and suspected killings follow reports this week of public executions and the discovery of mass graves containing the bodies of tribesmen killed by ISIS.

The bodies of an estimated 200 members of Albu Nimr were found in a mass grave just outside Hit, a senior Iraqi security official told CNN. The tribesmen were captured by ISIS fighters after it took control of the area, the official said.

Another 48 tribesmen were marched through the streets of Hit before they were publicly executed, the official said.

And a mass grave was found in nearby Ramadi, according to Iraqi media accounts. Video of those executions had been uploaded to the Internet.

"We are deeply concerned by reports of mass executions of Sunni tribesmen in Anbar province by ISIL and strongly condemn the brutal actions that ISIL continues to perpetrate against the Iraqi people," U.S. State Department spokeswoman Jen Psaki said.

"...ISIL's indiscriminate crimes prove, yet again, that it is targeting all Iraqis, regardless of faith or region."

Albu Nimr fights back

Albu Nimr is known for its fighting skill and resistance.

A 2003 Brookings Institution report observed that, though most Iraqi Sunni tribes were loyal to Saddam Hussein in the days when he ran the country, the Albu Nimr tribe had mounted a protest against the former Iraqi strongman in 1995 after the execution of a noted member. The protest was put down by paramilitary forces loyal to Saddam.

In general, however, Saddam respected the Albu Nimr.

Since Saddam's fall, they've been tapped to oppose al Qaeda in Iraq. They were also part of last year's Sunni uprising against the former Prime Minister Nuri al-Maliki and his Shiite-dominated government.

They have been fighting ISIS but say they haven't received much support from the Iraqi government and international coalition members.

It isn't just Abu Nimr that's being eliminated. Earlier this week, it was reported that when IS took control of the city of Mosul last June, they went into the prison and executed at least 600 inmates - mostly Shiites. The massacres have a point, of course; fear. Instilling fear in the populace keeps them docile. Instilling fear into Iraqi soldiers makes them abandon their positions and run at the sight of them. It's barbaric. But very effective.

Islamic State is not out to win hearts and minds. "Join or die" is proving to be an extremely effective tactic which allows them to post a minimum number of fighters in most towns while the bulk of their forces engage the Iraqis.Can the US do anything to stiffen the backbones of Iraqi troops and help them stand up to IS? It would take a minor miracle to effect that kind of change.