Egypt's Muslim Brotherhood's Supreme Guide Mohamed Badie has suffered a heart attack in Tora prison, where he is currently being held pending trial, a security source told Ahram Arabic news website.
The Interior Ministry – in a statement Saturday – denied rumours Badie has died.
According to the security source, Badie's condition is thus far stable and a team of doctors were sent to the prison to examine him.
Badie, along with most of the group's top figures, have been arrested following the ouster of President Mohamed Morsi – a leading figure in the group - by the military on 3 July following mass protests against his rule.
Badie and his deputies have been charged by prosecutors with 'inciting murder' of anti-Morsi protesters. The first session in the trial was held on 25 August.
Security forces have also carried out mass arrests against hundreds of the group's middle-ranking leaders and members.