Thousands of supporters of Egypt's Muslim Brotherhood are demonstrating in a Cairo square, waving pictures of ousted president Mohammed Morsi.
They are chanting anti-military slogans, calling the army chief a traitor. He led the military's removal of Mr Morsi from office last week.
The unseating of Mr Morsi followed demonstrations by millions of Egyptians against his rule. It was a bitter blow to the Brotherhood, which won a string of ballots, including Mr Morsi's election as president.
One speaker at today's demonstration pledged to stay on the streets until Mr Morsi is reinstated.
"We are ready to stay for a month, two months, a year or even two years," ultraconservative Islamist Salafi cleric Safwat Hegazi told protesters.
This week more than 50 pro-Morsi protesters were killed in a clash with the military.
Earlier prosecutors said they will investigate allegations that Mr Morsi escaped from prison during the 2011 revolution against the rule of dictator Hosni Mubarak with help from the Palestinian militant group Hamas.
Chief prosecutor Hesham Barakat has received testimonies from a court in the Suez Canal city of Ismailia that will be the base for a probe into the jailbreak by Mr Morsi and more than 30 other Muslim Brotherhood leaders.
The question of whether Hamas helped them escape amid the chaos surrounding the 2011 uprising has been debated in the media for months.
It proved a political headache for Mr Morsi during his one-year rule as Egypt's first freely elected president. Critics in the opposition and judiciary have suggested that proof of foreign intervention on Egyptian soil could lead to treason charges.
The toppled Islamist leader has been kept at an undisclosed Defence Ministry facility and no charges against him have been announced.
Hamas has denied any role in the January 29, 2011, jailbreak at Wadi el-Natroun prison north-west of Cairo.
Mr Morsi and other Brotherhood leaders have said local residents helped them escape after most inmates left the jail.
News of the intended investigation came a day after the authorities issued arrest warrants for the Brotherhood's spiritual leader, Mohammed Badie, and nine other Islamists accused of inciting violence after deadly clashes.
The warrants drew an angry response from the Brotherhood, which said "dictatorship is back" and insisted it will never work with the interim rulers.
Mr Badie's whereabouts are not known, but many of the others are believed to be taking refuge near a sit-in by the group's supporters outside the Rabaah al-Adawiya Mosque in a Cairo district that is a Brotherhood stronghold.