The top leader of Egypt's Muslim Brotherhood, Mohamed Badie, is reported to have suffered a heart attack while in jail.
However, state-run news agency MENA is denying the report from the private al-Nahar website that he had died.
Mr Badie and many other Muslim Brotherhood leaders have been arrested in recent weeks in one of the toughest crackdowns the Islamist group has faced.
He was charged in July with incitement to murder in connection with protests before Mohamed Morsi was ousted as president.
Mr Badie was due to be questioned on 28 August but prison authorities delayed the session because of his poor health, Reuters reports.
The Interior Ministry's Facebook page says Mr Badie is "enjoying good health". It is not clear whether the ministry was denying just the death or the death and the heart attack.
State-run al-Ahram newspaper reported earlier that Mr Badie suffered a heart attack while in jail but his condition had since stabilised.
Reuters says any severe deterioration in Mr Badie's health in prison would certainly deepen hostilities between the Muslim Brotherhood and the army-backed Government.