World leaders have condemned the beheading of British hostage Alan Henning by the Islamic State of Iraq and the Levant, after the fourth such video was released on the Internet

The murder of Alan Henning is absolutely abhorrent, it is senseless, it is completely unforgivable. There is no level of depravity to which they will not sink.

British Prime Minister David Cameron

British Prime Minister David Cameron said on Saturday that the slaying of the aid worker demonstrates the necessity of destroying ISIL, which is currently being targeted with air strikes by a US-led coaltion in Iraq and Syria.

"The murder of Alan Henning is absolutely abhorrent, it is senseless, it is completely unforgivable," Cameron said. "There is no level of depravity to which they will not sink. No appeals made any difference.''

Henning, a 47-year-old taxi driver from the town of Eccles in northwest England, was snatched minutes after his aid convoy entered Syria in December 2013. 

The United Nations also condemned Henning's killing on Saturday.

"This crime is a tragic reminder of the increasing dangers volunteer humanitarian personnel face every day in Syria," Maria Cristina Perceval, the Argentinian ambassador to the UN and acting Security Council president, said.

"It also once again demonstrates the brutality of ISIL which is responsible for thousands of abuses against the Syrian and Iraqi people."

More threats

The US said on Friday that the video is another example of the brutality of the group, and reiterated its military operation to "degrade and destroy ISIL". 

The video was released in the same manner as other ISIL videos and the masked, British-accented, English-speaking, man sounded similar to the one who carried out the other slayings.

The fighter directly addresses US President Barack Obama, before killing his victims, who include American reporter James Foley, American-Israeli journalist Steven Sotloff, British aid worker David Haines and now Henning.

"Obama, you have started your aerial bombardment of Sham [Syria], which keeps on striking our people, so it is only right that we continue to strike the neck of your people," the masked man in the video said.

The video ended with an ISIL member threatening a man identified as an American named Peter Kassig.

Source: Al Jazeera and agencies