A video purporting to show the killing of US aid worker Peter Kassig by Islamic State in Syria has been posted on the internet.

The footage has not been verified and it is not known when it was recorded.

It appears to show a militant, who has become known as Jihadi John, amid reports he has been wounded during US airstrikes in Iraq. The UK's Foreign Office is investigating the reports.

In the video, the black-clad militant stands before a severed head that he claims is that of Mr Kassig.

Speaking in English in a British accent, the man says: "This is Peter Edward Kassig, a US citizen."

The Foreign Office said it is aware of the video and is analysing it.

A spokesperson said: "If true, this is a further disgusting murder."

Mr Kassig's family has released a statement saying “we are aware of the news reports being circulated about our treasured son and are waiting for confirmation from the government as to the authenticity of these reports. We will have no other statement at this time and ask that you please respect our privacy.

"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," they add.

Ed and Paula Kassig are also asking the media and individuals to avoid playing into the hostage takers hands and refrain from publishing or broadcasting photographs or video distributed by them.

Previous videos have shown a desert landscape, but in the latest footage the IS militant appears to be in front of a town with fields in the distance.

The video also shows what appears to be the mass beheading of a number of captured Syrian soldiers.

Mr Kassig, a former soldier, was threatened at the end of a video showing the beheading of British aid worker Alan Henning in October.

The 26-year-old from Indiana was taken hostage in October 2013.

He had returned to the region as a charity worker after serving in Iraq in 2007.

His family says that Mr Kassig converted to Islam after being captured and had taken on the first name Abdul-Rahman.

In October, his parents released this video message:

Originally published at 10.21am