Opposition leader Mohamed ElBaradei said Egypt's Islamist President Mohamed Morsi bore "full responsibility" for violence that erupted on Wednesday, and that his regime was losing more legitimacy each day.
ElBaradei, the former head of the UN nuclear agency, said the opposition was "ready for dialogue" on condition that a decree expanding Morsi's powers be rescinded and a December 15 referendum on a disputed constitution scrapped.
"We will not sit down for any dialogue without the cancellation of the constitutional declaration," he told reporters, describing Morsi's regime as "oppressive and autocratic".
"The revolution did not happen for this. It happened for freedom, democracy and human dignity," said ElBaradei, who heads the National Rescue Front with former Arab League chief Amr Mussa and ex-presidential candidate Hamdeen Sabbahi.
"Morsi must listen to the people, whose voice is loud and clear. There is no legitimacy in excluding the majority of the people. There is no legitimacy in enabling one group to dominate Egypt," he said in reference to the Muslim Brotherhood, on whose ticket Morsi ran for office.
His comments came as supporters and opponents of Morsi clashed outside the presidential palace in Cairo.