The leader of the Muslim Brotherhood general guide Mohammed Badie has been arrested, according to the Egyptian government.
The arrest could see further spikes in violence between Brotherhood members and the interim government.
Three days of mourning are taking place in Egypt following the killing of 25 policemen in Sinai by suspected militant Islamic groups. The murders followed the killing of 36 Islamists being held in police custody.
The brotherhood has rejected the charges against Badie as fabricated with no legally acceptable evidence.
Approximately 900 people have been killed in Egypt since the government crackdown on 14 August, when the army cleared pro-Mursi protest camps that have been in place for weeks on two of Cairos squares. The rising death toll includes Muslim brotherhood members as well as police officers and soldiers.
The camps were set up in protest at the 3 July military ousting of former president Mohamed Mursi.
The Muslim Brotherhood is being labelled as a terrorist organisation by the interim government and there have been proposals made to place a new ban on the group.
News has also emerged that former president Hosni Mubarak, overthrown in the 2011 revolution, could be released from jail. Several corruption charges against him have been dropped. However, he still faces charges for complicity in the killing of peaceful protesters in 2011.