Jama'a al-Islamiya and its political arm, the Construction and Development Party, have called on interim President Adly Mansour to resign in attempts to ease tension and spare Egypt further violence.
Mansour, who started his term as head of the Supreme Constitutional Court on 1 July, became Egypt's interim president when an army takeover, some argue forced by popular pressure on the streets, removed Mohamed Morsy from the presidency.
Morsy's supporters have vehemently condemned the move as a military coup, stressing the ex-president carried legitimacy as Egypt's first freely elected leader. Both opponents and supporters have clashed for days, leaving dozens killed and over a thousand more injured.
Jama'a al-Islamiya described Mansour as "illegitimate" and an "appointed" leader, urging him to step down to halt the risk of "a dire conflict" in Egypt, in a statement Sunday.
The Islamist group said it had thought Mansour would “reject [the] interim presidency and refuse to suspend a constitution approved by nearly 64 percent of Egyptians."
It said Mansour’s resignation represented “the proper way out from the current crisis."
Earlier on Sunday, prosecutors summoned group leaders, Tarek al-Zomor and Assem Abdel Maged, for questioning over their alleged role in inciting violence between Morsy's supporters and opponents at Bein al-Sarayat near Cairo University on Tuesday, which left at least 21 dead.
Edited translation from MENA