Cairo - Egypt's army is "preventively" holding ousted president Mohamed Morsi after his ouster by an army decree, a senior army official told AFP on Thursday.
"He is being held preventively for final preparations," the official said, suggesting Morsi might face formal charges over accusations made by his opponents.
Morsi was detained along with senior aides after issuing a defiant call for supporters to protect his elected "legitimacy", in a recorded speech hours after the military announced he had been ousted on Wednesday.
"We had to confront it at some point, this threatening rhetoric," the military official said.
"He succeeded in creating enmity between Egyptians," the official said.
At least 50 people were killed in clashes in the days leading to massive protests on 30 June calling for his departure.
That prompted the army to issue the president a 48-hour ultimatum to find an agreement with the protesters.
Morsi has been summoned for questioning by a court over his escape, along with other inmates, from prison during the revolt that overthrew his predecessor Hosni Mubarak in 2011.
The military official suggested he may now be charged by prosecutors in the case.
A senior member of Morsi's Muslim Brotherhood has earlier told AFP Morsi and senior aides had been detained in a military facility.
"Morsi and the entire presidential team are under house arrest in the Presidential Republican Guards Club," Gehad El-Haddad, the son of a top Morsi aide, told AFP.
Haddad's father, Essam El-Haddad, widely seen as Morsi's right-hand man, was among those held, he added.
The military official did not specify where Morsi is being held. Haddad said the ousted president was separated from his aides and detained at the defence ministry.
Morsi's top aides have switched off their phones. Other presidential aides who were separated from Morsi earlier in the day say they have lost communication with their leader.
He had earlier been at his office in the Republican Guard's headquarters, before he was moved.
A police general told AFP that security forces were seeking to arrest leaders of his Muslim Brotherhood movement.
Police have already arrested Saad al-Katatni, head of Morsi's Freedom and Justice Party, and Rashad Bayoumi, the Muslim Brotherhood's deputy supreme guide, the general said.
Hours after the military announced it had cancelled the constitution and would appoint the head of Egypt's top court as interim president, Morsi issued a defiant call to arms in a pre-recorded speech aired on Al-Jazeera television.