Islamic State (IS) has threatened to kill American hostage Peter Kassig next, after releasing a video showing the murder of British aid convoy volunteer Alan Henning.

The former soldier appeared at the end of a YouTube clip which showed the killing of Mr Henning by IS, which is also known as ISIS or ISIL.

An IS fighter says in the video: "Obama, you have started your aerial bombardment in Sham. So it's only right we continue to strike the necks of your people."

Speaking after the video was released, President Barack Obama said: "The United States strongly condemns the brutal murder of United Kingdom citizen Alan Henning by the terrorist group ISIL.

"Mr Henning worked to help improve the lives of the Syrian people and his death is a great loss for them, for his family and the people of the United Kingdom.

"Standing together with our UK friends and allies, we will work to bring the perpetrators of Alan's murder - as well as the murders of Jim Foley, Steven Sotloff and David Haines - to justice.

"Standing together with a broad coalition of allies and partners, we will continue taking decisive action to degrade and ultimately destroy ISIL."

Lisa Monaco, Homeland Security adviser to the White House, described Mr Henning's murder as "yet another clear example of the brutality of this group", which has previously killed two American journalists - James Foley and Steven Sotloff.

Mr Kassig, who is in his mid-20s and from Indiana, went to the region to volunteer in hospitals in Lebanon after serving in Iraq.

After spending time in Lebanon, Mr Kassig then set up his own charity to deliver aid to Syrians - Special Emergency Response and Assistance (SERA).

Mr Kassig was undertaking a project for SERA when he was detained on 1 October 2013 on his way to Deir Ezzour in eastern Syria.

His family say that Mr Kassig has converted to Islam since being captured and has taken on the first name Abdul-Rahman.

Former hostages have told them that his faith has given him comfort in captivity.

In a statement his parents, Ed and Paula Kassig, said: "The Kassig family extends our concern for the family of Alan Henning.

"We have read about his work and his generous character with great respect and admiration.

"We ask everyone around the world to pray for the Henning family, for our son, and for the release of all innocent people being held hostage in the Middle East and around the globe."

SERA has suspended operations while efforts continue to secure Mr Kassig's release.