Egyptian prosecutors are to question ousted president Mohamed Morsi and other top Muslim Brotherhood leaders over "crimes" committed during the earlier uprising against former dictator Hosni Mubarak.
The move comes days after Morsi himself was pushed out by the powerful army swiftly followed by the installation of an interim president.
Morsi remains under arrest and is likely to be grilled over a series of alleged crimes during the January 2011 revolution spearheaded by the Brotherhood.
According to a source quoted by Ahram Online, Morsi will be questioned for allegedly encouraging mob violence, getting police officials murdered and appointing gunmen to kill protesters.
Saad el-Katatni, the chief of the Freedom and Justice Party, the political arm of the Brotherhood, and the deputy head Essam el-Erian, will also be questioned, suggest reports.
In addition, Brotherhood leaders will be questioned for allegedly seeking the help of operatives from the Lebanese militant group Hezbollah and the Palestinian outfit Hamas.
The whereabouts of Morsi are still unclear, although local reports speculate he is being confined at the defence ministry headquarters.
The Brotherhood's deputy, Khairat el-Sahter, has also been apprehended by the army for allegedly inciting violence two days after Morsi was taken into custody.
However, the presidential spokesman struck a conciliatory note at his latest press conference. "We extend our hand to everyone, everyone is a part of this nation. The Muslim Brotherhood has plenty of opportunities to run for all elections including the coming presidential elections or the ones to follow."
As the turmoil looks set to continue, the appointment of liberal politician and Nobel laureate Mohamed ElBaradei as interim prime minister, which was confirmed by several sources, has been withdrawn after Islamists objected to the decision.
More violence is expected as the supporters and opponents of the Brotherhood have called for protests across Egypt later in the day.
The Brotherhood-led National Alliance has urged its supporters to turn up in large numbers at rallies to "protect the revolution".
Thousands of protesters are expected to take part in the demonstrations, heightening fears of further violence.