Isis jihadi beheads four Kurdish fighters in brutal execution video

Roberts, who goes by the nickname "Red", is among the most experienced fighters here - a former specialist with the 25th Infantry Division, he did two tours of duty with the U.S. Army in Iraq.

"Obama, you have learned a new lesson", he said. "Six of the soldiers of the caliphate faced 400 of your children; they killed and injured them by Allah's grace".

Three other jihadis - all dressed in black with their faces covered - are also seen holding blades as they stand behind three other Kurds wearing orange jumpsuits.

Defense Secretary Ash Carter said Friday the decision to send special operations forces to Syria to work with local Kurdish and Arab fighters is unlikely to be the last significant adjustment to the USA fight against the resilient Islamic State group.

Blitzer: Have you told this to officials at the White House? When you look at the groups that are on the ground there, the most effective fighting groups who are fighting to overthrow the Syrian government of Bashar Assad, they are predominantly ISIS, al-Qaeda, al-Nusra and these other Islamist extremist groups. "However we have now another message for them".

Roberts says it's crossed his mind many times that he too could be killed, but that's a price he's willing to pay.

"We hold 215 ISIS prisoners and we treat them according to worldwide human rights laws", he said. President Obama, sold to the American public as the candidate who would end the hated Iraq war, is now committing United States troops to combat operations on an open-ended timeline, not just in Afghanistan, but also in Iraq and Syria. "We do not kill our prisoners".

A former US soldier now battling Isis in Syria has warned others thinking of joining the fight not to expect it to be like a computer game.

The "actionable intelligence" in that case proved faulty, as none of the Kurdish hostages being sought were present at the site, and many of those "rescued" turned out to be ISIS members being held by the Islamist militia as suspected spies.

The terrorist, whose real name is believed to be Mohammed Emwazi, is considered to be a priority target after killing American, Western, and Japanese hostages.

According to the groups, Raqqa is Being Slaughtered Silently and Eye on Homeland, activists Ibrahim Abdul Qadir and Faris Humadi the men who were shot and beheaded. ISIS has not yet claimed responsibility for their deaths.

Carter said the U.S. forces in northern Syria will be in an area where Russian warplanes are not bombing, so it would not be necessary to talk to the Russians about steering clear.