Facebook is investigating after the account of a neo-Nazi who planned to kill an MP remained active despite the company saying it would be deactivated.
Last week the social media giant announced a series of far-right Facebook pages would be removed.
One of those it named - Jack Renshaw, 23, from Skelmersdale in Lancashire - is awaiting sentencing after admitting a terrorist plot to murder a Labour MP.
But his personal profile remained live until the BBC raised it with the firm.
Those banned from Facebook last week - in an announcement that received significant publicity - include the British National Party, the former BNP leader Nick Griffin, and the National Front.
The social network said it had taken action because those involved proclaimed a "violent or hateful mission".
"Individuals and organisations who spread hate, or attack or call for the exclusion of others on the basis of who they are, have no place on Facebook," the company said.
But Renshaw's account, which was linked to other extreme right figures, remained active.
Renshaw pleaded guilty at the Old Bailey to preparing to murder his local MP, Rosie Cooper, with a machete and threatening to kill a female detective.
He will be sentenced next month, but is already serving time after being convicted last year of sexually grooming adolescent boys and stirring up racial hatred in speeches.
Before being arrested he used Facebook to declare himself a "Nazi terrorist".
At one stage fellow activists created a "unity group" for Renshaw in which he stated - in a reference to Thomas Mair, the man who killed MP Jo Cox - that he was going to "Mair" others.
Facebook only removed Renshaw's account - bearing his picture and which featured in his trial - hours after the BBC contacted the company to say it was still active.
It said: "We design our policies to keep people safe on Facebook and we are very sorry to have discovered an additional account for Jack Renshaw. "The account in question managed to elude our systems by using a different identity.
"We have taken immediate action to remove this profile, which is in addition to the accounts associated with his name that we removed on 18 April," Facebook added.
MPs on Wednesday challenged Facebook for not doing enough to remove videos of the Christchurch mosque attacks and was asked why so much neo-Nazi content is available.