The jihadist group Islamic State has released a video appearing to show the beheading of a Kurdish man in the Iraqi city of Mosul, which the group captured in June.
The video "A Message in Blood" shows several men in orange jumpsuits said to be captured Kurdish fighters.
The jihadists warn that others will be killed if Kurdish leaders continue to back the US.
Kurdish Peshmerga fighters from the autonomous Kurdistan Region of northern Iraq have been trying to stop an advance by IS.
The US has launched a series of air strikes to try to hamper IS efforts.
Last week, IS released a video showing the beheading of US journalist James Foley.
The group said it plans to kill other US hostages in retaliation for the air strikes in Iraq.
The militants and Kurdish and Iraqi forces are battling for the Mosul dam - the largest in Iraq.
It is an important strategic resource as it controls most of the country's water and power.