Abedi was jailed for at least 55 years for helping plan the attack which killed 22 people in 2017
Hashem Abedi, the brother of Manchester Arena attacker, Salman Abedi, has attacked and wounded three prison officers.
Abedi threw hot cooking oil over the officers before producing “home-made weapons” and stabbing them, said the POA, a trade union covering prison staff.
The officers sustained life-threatening injuries including burns, scalds and stab wounds in the “unprovoked” and “vicious” attack, it added.
The Prison Service confirmed three prison officers were treated in hospital after an attack by a prisoner at HMP Frankland, County Durham.
One female officer was discharged by 4pm on Saturday.
A Prison Service spokesperson said: “Three prison officers have been treated in hospital after an attack by a prisoner at HMP Frankland.
“Police are now investigating so it would be inappropriate to comment further.
“Violence in prison will not be tolerated, and we will always push for the strongest punishment for attacks on our hardworking staff.”
This story is being updated.