Ousted Egyptian president Mohamed Morsi has refused to answer questions on allegations he leaked top secret documents to Qatar, Al-Ahram Arabic newspaper reported.
Morsi's detention has been extended for another 15 days pending further investigations into the matter.
He is accused of smuggling top secret documents to Qatar via Al Jazeera TV channel and his staff, including his personal secretary, Amin El-Serafi.
Morsi refused to answer prosecutors' questions because he was the "legitimate president."
Investigators went to Tora Prison on Wednesday to question Morsi, state news agency MENA reported.
Morsi, who was removed from power by the army in July 2013 amid nationwide protests against his year-long rule, also faces a number of other charges in separate trials, including espionage and inciting the murder and torture of opposition protesters outside the presidential palace in December 2012.