Egypt's prosecution on Monday ordered the detention of 255 members of the Muslim Brotherhood pending investigations of a range of allegations, including murder, attempted murder, thuggery, vandalism and arson.
Another 359 are being questioned following their arrest on Saturday during Al-Fath Mosque siege in Cairo's Ramses Square, Al-Ahram Arabic new website reported.
All the accused were arrested in Cairo during 2 days of anti-government protests by supporters of deposed president Mohamed Morsi.
Rallies started on Friday when deadly clashes between security forces and demonstrators erupted across the country after two pro-Morsi sit-ins were violently dispersed by police last Wednesday.
Since Wednesday, the official death toll has surpassed 850. The majority of causalities reported were protesters.
Violence has soared in Egypt after the dispersal of the pro-Morsi sit-ins as police confronted angry protesters, who attacked police stations, government buildings and churches.
A new wave of arrests of pro-Morsi activists and Islamist figures ensued following the events.
In a press conference held Monday at the Doctors Syndicate, a top Muslim Brotherhood member, Ahmed Abu Baraka, said that more than 400 leading members have been arrested since Wednesday. Abu Barka added that the members do not have lawyers to represent them.
On Saturday, Egypt's interior ministry announced that it had arrested over 1,000 protesters and Islamist figures, raising widespread concerns about an all out crackdown on the Muslim Brotherhood and its allies and possibly damaging hopes of future reconciliation.
Meanwhile, the Muslim Brotherhood defiantly called for a week of protests, planning over 9 marches on Monday to reject what they describe as a "coup" by the military to take over power and demanding Morsi's reinstatement.
On Sunday, at least 36 pro-Morsi detainees were killed while being transferred to Abu Zaabal Prison north of Cairo. The interior ministry said they asphyxiated when police fired teargas to abort an escape attempt.
The Muslim Brotherhood said that the interior ministry's account of the killings has not been verified and accused security forces of "executing" the prisoners for their rejection of the "military coup."
The transitional Egyptian government declared a state of emergency for a period of one month last week following the violent dispersals. The state of emergency is now accompanied by a nighttime curfew that the government said would be gradually reduced.
Egypt's government has sharpened its rhetoric against the Brotherhood, contending that it is fighting a "terrorist plot" being carried out by the group.
The European Union is holding an emergency meeting on Monday to review relations with Egypt following the bloodshed the country has witnessed during the past week.
Some EU governments have warned cutting potential aid to Egypt as a result, but the latter was reassured by Saudi Arabia that it would step in to replace any aid held back by Western nations.