London-based imam and journalist Ajmal Masroor
Several prominent British Muslims said police have warned they may be in danger, after they were named as enemies of Islam in a video purportedly made by extremists linked to Somalia's Shebab militants.
Police said it was investigating the hour-long film, which was posted on YouTube on Wednesday but has since been removed.
"We're aware of the video reportedly released by al-Shebab," a Scotland Yard spokesman told AFP.
"We are currently assessing its content. A number of individuals have been spoken to following the release of the video."
At least four Muslim commentators -- all of whom have spoken out against extremism -- said they had been visited by police after being named in the film.
The US-based monitor SITE Intelligence Group had identified the video as having been produced by the Shebab, the Somali group that claimed responsibility for a bloody attack at a Nairobi shopping mall last month.
Reportedly narrated by a man with a British accent, it singled out the commentators as having "mutilated the teachings of Islam", according to the Guardian newspaper.
Ajmal Masroor, a London-based imam and journalist, wrote on his Facebook page that police had told him "to be more vigilant".
"The basic message... was that my life was in imminent danger from the terrorists," he wrote.
He added: "I shall speak out loud and clearly against extremism and terrorism no matter how many threats I receive."
Mohammed Ansar, a filmmaker and journalist, said police were now regularly patrolling outside his home.
"In between locksmiths, security people and interviews," he wrote on his Twitter page.
"It is quite a thing to have your faith and values truly put to the test. To have your life and those you love, at risk. Quite a thing."
Commentator Mohammed Shafiq and Usama Hasan, a senior researcher for the anti-extremist think-tank Quilliam, also said they had received visits from the police.
The video was titled "The Woolwich Attack: It's an Eye for an Eye" in reference to the British soldier who was hacked to death in Woolwich, southeast London, on May 22.
Two Muslim converts are due to stand trial for the murder next month.
The video encouraged Muslims to carry out attacks on British soil, according to reports, as well as identifying 11 Britons who it said had died fighting for the Shebab.