Islamic State 'kills US hostage' Steven Sotloff

Islamic State has released a video online which purports to show the beheading of Steven Sotloff, a US journalist being held hostage by the militants.

Mr Sotloff disappeared in Syria in 2013. He was shown at the end of a video last month showing fellow US journalist James Foley being killed.

The White House said US officials were checking the reports.

BBC security correspondent Frank Gardner describes what the video shows.