British Muslims who speak out against extremism are being warned that they could be targeted by members of the Somali militant group al-Shabab.
British Muslim commentator Mohammed Ansar said he was currently under police protection because of what he was told was a "credible threat".
It comes after al-Shabab militants posted a video online which named Muslims who have criticised jihadists.
Scotland Yard said it was investigating the video.
The hour-long film is narrated by an unidentified man with a British accent.
It praises acts of Islamist terrorism.