US hostage Aid worker Abdul Rahman 'killed by IS'

A video posted online claims to show that Islamic State militants have killed the captured US aid worker Abdul-Rahman Kassig. The video shows a masked man standing over a severed head which he says is that of Mr Kassig. The US says it is working to determine the authenticity of the video, which also shows a mass beheading of 18 Syrian troops.

Mr Kassig, also known as Peter, was captured last year. His family, who live in the US state of Indiana, said they were awaiting confirmation of the reports about their "treasured son". "We prefer our son is written about and remembered for his important work and the love he shared with friends and family, not in the manner the hostage takers would use to manipulate Americans and further their cause," the family said in a statement. 

This is perhaps the most elaborate and graphic of all the murder videos posted online by IS. Much of it is taken up with a recent history lesson on Iraq and Syria as seen through the eyes of the jihadists. But the latter part shows the beheading of 18 Syrian prisoners in revolting, lingering detail. Unlike earlier videos, this one revels in gore. Amongst the boiler-suited captives murdered in cold blood is a man IS says is the former US soldier Peter Kassig, who converted to Islam and changed his name to Abdul-Rahman. Neither his conversion, nor the fact that he was helping refugees when he was captured a year ago, appear to have saved him.

Mr Kassig's murder is a sign of frustration that IS militants are unable to hit back at the coalition air strikes that have driven them off key sites like the Mosul and Haditha dams, and prevented them from seizing the town of Kobane.

Unlike similar videos released in the past, the latest shows the faces of many of the jihadis. It also at one point gives a specific location - near Dabiq in Aleppo province, with an identifiable village in the background.

The latest video did not show the person identified as Mr Kassig being beheaded. Also unlike previous videos, it did not show other Western captives or directly threaten to behead anyone else.

The US National Security Council said it was investigating the video, and would be "appalled by the brutal murder" if it was confirmed. IS has previously murdered four Western hostages - British men Alan Henning and David Haines, and US journalists James Foley and Steven Sotloff. Those killings were carried out by a man believed to be British. That man bears a resemblance to one of the masked militants pictured in the video purporting to show Mr Kassig.