Michael Adebolajo was injured during the
incident in Belmarsh prison
Woolwich murder suspect Michael Adebolajo was forcefully pushed against a window by prison officers, knocking out teeth, his brother has claimed in an interview with the BBC.
Jeremiah Adebolajo said he spoke to his brother on an almost daily basis.
Five staff at Belmarsh Prison have been suspended and a police investigation has begun into the incident.
But the Prison Officers Association (POA) has strenuously denied its members did anything wrong.
The say the officers used approved restraint procedures.
Michael Adebolajo is accused of killing Fusilier Lee Rigby in May.
'Smashed his head'
During the interview with the BBC's Tom Symonds, his brother Jeremiah said: "I wonder why it took five prison officers to restrain one man and how in the course of that restraint his teeth were able to be knocked out if they were following procedures.
"The suggestion is that procedures means that prisoners' teeth are going to be knocked out."
Jeremiah Adebolajo said he speaks to his brother almost daily, and had also spoken to his lawyer, and to the governor of Belmarsh Prison. He had also discussed the incident with the suspect's sister - who received a call from Michael Adebolajo minutes after it happened.
According to Jeremiah Adebolajo his brother said five officers at a time are present when dealing with him and he is never in contact with any other prisoner. He says the altercation began when Michael Adebolajo was given an instruction by one of the guards.
"They decided to twist his arm back... the arm that had been shot.... He manoeuvred out of that so they smashed his head against a window," he said.
Speaking on BBC Radio 4's Today programme on Saturday, POA chairman Peter McParlin said: "The reports that were initially put out to the press were saying that the prisoner had been attacked.
"Prison staff do not attack prisoners. We feel that the Ministry of Justice missed an opportunity to correct false reporting of events at Belmarsh."
He said that, although restraint techniques were designed to minimise injuries to staff and prisoners, "sometimes there are unforeseen consequences in any violent incident".
'Control and restraint'
Earlier, he had said: "We are absolutely confident, having spoken to our members, that they will have been found to have done absolutely nothing wrong at all.
"The fact that that prisoner has a certain amount of notoriety makes no difference to them, because they're professionals, and they deal with every prisoner in the same way, using control and restraint, which are officially accepted methods to be used within prison, when dealing with prisoners on occasion that need to be restrained."
The POA says the incident was covered by CCTV cameras which would show clearly what had happened.
According to Ministry of Justice guidelines for the prison service, "control and restraint techniques" must only be used as a "last resort after all other means of de-escalating (e.g. persuasion or negotiation) the incident, not involving the use of force, have been repeatedly tried and failed".
"Staff must continue to attempt to de-escalate the situation throughout the incident with the aim of releasing holds and locks," the guidelines continue.
"The application of C&R holds may cause pain to a prisoner and if the prisoner is compliant, the holds must be relaxed."
A police spokesman said: "We can confirm that an allegation of assault was passed to the Metropolitan Police Service on 17 July by Belmarsh Prison. An investigation has been started."
A prison service spokesman said five members of staff had been suspended "while the police investigation is ongoing".
Prison Service procedures state that this should only happen in 'exceptional cases'.
Michael Adebolajo was not given immediate medical treatment for the injury to his mouth following the incident and Jeremiah Adebolajo said he found that "strange".
However, a Prison Service spokesperson said: "Following an incident at Belmarsh prison on 17 July a doctor attended. The prisoner refused medical treatment initially but was subsequently treated by healthcare staff."
The Prison Service would not comment further on the allegations made by Jeremiah Adebolajo.