Sky News understands that one of the prisoners believed to be involved in an assault on prison officers at a maximum security jail was Brusthom Ziamani, who was jailed in 2015 for plotting to behead a soldier.
Ziamani and another inmate are understood to have been wearing fake bomb vests and carrying improvised weapons when they carried out Thursday's attack at HMP Whitemoor in Cambridgeshire.
Five prison staff were injured and taken to hospital.
Anti-terror police have launched an investigation.
A Prison Service spokesman said the incident was "quickly resolved by brave staff - and our thoughts are with the injured officers at this time".
He did not state the nature of the injuries but Sky News' crime correspondent Martin Brunt said: "According to a witness the fake suicide vests were, on first sight, realistic, with batteries attached and wires dangling.
"The first officer was seriously injured, stabbed several times on a landing. Other officers were also stabbed and one suffered a broken eye socket."
A witness said: "It was brutal. There was a lot of blood."
Brunt said the attack will "raise old concerns about radicalisation inside Whitemoor, which houses some of Britain's most dangerous terrorists".
And he added that he understood the stabbings - thought to be the first terror attack inside a British prison - were being taken "so seriously that Boris Johnson was briefed on it".
The Prison Service statement added: "We do not tolerate assaults on our hardworking officers and will push for the strongest possible punishment.
"We have referred the incident to the police and it would be inappropriate to comment further at this time."
Muslim convert Ziamani, from Camberwell, southeast London, was jailed for 22 years for hatching a plot to behead a UK soldier inspired by the murder of Fusilier Lee Rigby.
He was arrested by counter-terrorism officers in August 2014, carrying a rucksack containing a 12-inch knife, a large hammer and an Islamic flag.
He had told a security officer at Wandsworth Prison in London that he had been on his way to "behead a British soldier at an army barracks and hold the severed head in the air" when he was arrested.
The Old Bailey heard how he had earlier shown his ex-girlfriend weapons and described Fusilier Rigby's killer Michael Adebolajo as a "legend".