The head of the Egyptian army has announced the suspension of the country's constitution, which means President Mohammed Morsi is no longer in power, BBC reported.
General Abdul Fattah Al-Sisi, flanked by religious and military leaders, said Wednesday that the chief justice of constitutional court would take the powers of the presidency.
Anti-Morsi protesters in Cairo's Tahrir Square cheered in response to the speech.
The move followed four days of mass street protests against Morsi, and an ultimatum issued by the military which expired Wednesday.
TV stations belonging to Morsi's Muslim Brotherhood went off air at the end of the army chief's speech.
However, minutes later, a notice went up on Morsi's Facebook page denouncing the army move as a "military coup".
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BBC said Morsi's current whereabouts were unknown, but an unverified tweet urged civilians and members of the military to uphold the law and the constitution.
After Gen. Al-Sisi's address, both Pope Tawadros II - the head of the Egyptian Coptic Church - and leading opposition figure Mohammed ElBaradei made short statements.
ElBaradei said the new roadmap aimed for national reconciliation and represented a fresh start to the January 2011 revolution.
Later, the army was involved in a show of force, fanning out across Cairo and taking control of the capital, BBC said.
Thousands of anti-Morsi protesters on the streets of Cairo celebrated, with fireworks lighting up the night sky.
Meanwhile, Syrian President Bashar al-Assad said what was happening in Egypt was the falling of political Islam, Xinhua reported.
"Whoever uses religion for political gains or in favour of one party without the other will fall in every place of the world," Assad said in an interview with Syrian state-run al-Thawra newspaper.
"You can't fool everyone at the same time, so what would you think about the Egyptian people who carry the civilization of thousands of years along with clear pan-Arabism thinking," Assad said.
The president said that "after an entire year, the picture has become clear and the performance of the Brotherhood has helped in revealing the lies that they have spelled at the beginning of the popular revolution in Egypt".
The US said it was "very concerned" about the developments in Egypt.
The State Department blamed Morsi for not doing enough to steer his country out of the current crisis.
"We do, of course, remain very concerned about what we're seeing on the ground," State Department spokeswoman Jen Psaki said at a press briefing.
"And we do realise, of course, that is an extremely tense and fast-moving situation in Egypt."
Psaki said Morsi's speech Tuesday night lacked "significant steps" to resolve Egypt's worst crisis since the 2011 revolution that overthrew Hosni Mubarak.
"We have said that he must do more to be truly responsive and representative to the justified concern expressed by the Egyptian people," Psaki said.
"And unfortunately, that was not a part of what he talked about in his speech."
Earlier, in a phone call to Morsi, US President Barack Obama encouraged his Egyptian counterpart to respond to concerns voiced by protesters across the country.
Psaki said: "We believe all sides need to take steps to talk with each other, to engage with each other, to lower the level of violence and call for an end to the violence."