Amnesty International charges Shiite militias in Iraq are abducting and killing Sunni men to avenge attacks by Islamic State militants. In a report dated Tuesday, the human rights organization says the militias also are extorting money from the families of those they have kidnapped.

In recent months the extremist group also known as ISIS has overrun parts of Syria and Iraq, killing non-Sunni Muslim residents and forcing tens of thousands to flee their homes. The group also has been issuing propaganda videos depicting the beheadings of journalists and aid workers.

The Amnesty report says Iraqi government forces have been "unable or unwilling" to protect civilian populations from both ISIS' depredations and the militias, which "have been operating with unprecedented freedom and … impunity" in the wake of the ISIS onslaught.

Amnesty said it collected its information in six weeks of field research in northern and central Iraq during August and September. The report cites numerous incidents described by victims, their relatives and medical personnel.

Amnesty estimates more than 170 "mostly young Sunni men" have been abducted from the area around Samarra since June. Dozens have been found dead and others still are missing, the report said.

Amnesty said the militia actions constitute war crimes and condemned Baghdad's failure to control them. The group called on the government of Prime Minister Haider al-Abadi to take swift action to "reverse the phenomenon of militia rule, and establish the rule of law and respect for human rights without discrimination."