Rio Olympic bomb scare
A bomb disposal truck of the Federal Police is pictured outside the Carioca Arena 1 in io de Janeiro Mark Ralston/AFP/Getty Images

One of the 12 suspects imprisoned for allegedly pledging allegiance to Islamic State (Isis) and discussing bomb attacks at the Rio de Janeiro Olympics has been attacked in his cell.

Valdir Pereira da Rocha suffered brain death six hours after being beaten by fellow inmates at the Public Jail of Varzea Grande, in the Mato Grosso region of Brazil.

According to reports, the 36-year-old remains on life support and the decision to continue keeping his body functioning now rests with his family.

Da Rocha was arrested in July of this year and released on license with the condition that he wear an electronic anklet. However, he was arrested for another offence on 16 September and sent to prison, according to Globo.com.

On Friday (14 October), he was surrounded by other inmates in his cell and savagely beaten. An investigation is underway to determine the exact circumstances of the attack.

Da Rocha was initially arrested as part of Operation Hashtag, a counter-terrorism initiative launched by Brazil's Federal Police.

The other 11 suspects are in a separate penitentiary in the neighbouring state of Mato Grosso do Sul.

Authorities have described the 12 as "ill-prepared amateurs" who used social media to discuss possible attacks on the 2016 Olympic Games.

"Those involved participated in an online group denominated 'the defenders of Sharia' and were planning to acquire weapons to commit crimes in Brazil and even overseas," Justice Minister Alexandre de Moraes said at the time of the arrests.

"It was an absolutely amateur cell, with no preparation at all, a disorganised cell. A few days ago they said they should start practising martial arts, for example."

The ring is reported to have communicated via WhatsApp.

The Brazilian justice minister added that the group took part in an IS (Daesh) "baptism" online, shared execution clips with one another, and celebrated the terror attacks in Orlando and Nice.

One suspect made efforts to try and secure an AK-47 rifle in neighbouring Paraguay, but there was no evidence to suggest they had acquired any of the assault rifles.