LONDON- Islamic State jihadists mounted brutal offensives on both the Syrian battlefield and in their online propaganda war Friday, murdering a British hostage and attempting to storm a key border town.

In a video released by the group in response to US-led air strikes against it, a masked IS fighter beheads British driver Alan Henning and threatens a US captive, aid worker Peter Kassig.

The footage, almost identical to three previous execution films released by the group, inspired revulsion around the world and drew a stark warning from Britain's Prime Minister David Cameron.

"We will do all we can to hunt down these murderers and bring them to justice," he said, declaring that the apparent murder "shows just how barbaric and repulsive these terrorists are."

US President Barack Obama condemned the "brutal murder" and warned that the US-led coalition "will continue taking decisive action to degrade and ultimately destroy" IS.

The UN Security Council said the video serves as a "tragic reminder of the increasing dangers volunteer humanitarian personnel face every day in Syria."

SOURCE: AFP