One of the men who murdered Fusilier Lee Rigby is seeking compensation after he lost two front teeth when he was restrained by prison officers.
Michael Adebolajo claimed five prison officers assaulted him at London's high-security Belmarsh prison two years ago, but they were cleared of blame.
The Ministry of Justice (MoJ) said it would "robustly defend" the claim.
Adebolajo and Michael Adebowale are serving life for killing Fusilier Rigby near a London barracks in May 2013.
Adebolajo, 32, lost his teeth while he was being held at Belmarsh on remand after the killing near Woolwich barracks, and claimed he had been assaulted by the prison officers.
The officers were suspended from work, but were later told they had no case to answer.
The Prison Officers' Association insisted only approved techniques had been used in restraining Adebalajo.