The Prison Service has refused to comment on the detail of what is claimed to have happened when Woolwich murder suspect Michael Adebolajo was assaulted in prison on Wednesday.
A spokeswoman said: "The police are investing an incident that took place at HMP Belmarsh on July 17. It would be inappropriate to comment while the investigation is ongoing."
More top news
An eight-year-old boy who had to have both hands amputated as a toddler has been given the world's first double hand transplant.
Texas officials have released video taken in jail of Sandra Bland, the woman found dead in her cell three days after a controversial arrest.
A former member of the Bank of England's Monetary Policy Committee has told ITV News interest rates need to rise "sooner rather than later".