The Islamic State militant group has apologised for releasing the beheading video of US journalist Steven Sotloff before the official time, media reports said on Wednesday.

The video was shared through a Twitter account.

According to news site Vocativ, ISIS wrote on Justpaste "A clarification about the mistake made by 'Uyun al-Ummah' account, which published the video before it was supposed to".

"The user saw a tweet with the video and thought it was published officially. We tried to remove the video after we understood that his was published by mistake, and we are sorry to the followers of the Islamic State," the ISIS said.

In a later Twitter message, those responsible apologised and asked fellow jihadis not to 'reproach' them, the Daily Mail reported quoting Vocativ.

The video footage, depicting what the US called a sickening act of brutality, was posted two weeks after the release of video showing the killing of James Foley and just days after Sotloff's mother pleaded for his life.

Sotloff, a freelance journalist, was kidnapped in Syria in August 2013.

