Egyptian Defense Minister Gen. Abdel-Fattah el-Sissi, who doubles as commander in chief of the country's armed forces, said Wednesday night that President Mohammed Morsi, who was democratically elected last year, has been stripped of his authority.
The general said Morsi had not met the needs of the Egyptian people.
Morsi said via Facebook that the military's stripping of his authority is a coup d'etat and rejects the action. Morsi is in custody at the Ministry of Defense, according to French public radio.
In a televised address, the general said the constitution had been suspended and called for an early presidential election.
The military has agreed with representatives of political and religious circles on the need for a "roadmap" to governance, under which the head of the Supreme Constitutional Court chief Adly Mansour will take over the duties of president, while the heavily Islamic constitution will be revised.
An exact date for the next presidential election is yet to be set.
These developments came after several days of massive protests in Cairo by anti-government activists as well as supporters of Morsi, who was elected president in June last year in the country's first free and democratic presidential election since the February 2011 ouster of former leader Hosni Mubarak.
Following the announcement by the general, conflicts between the two sides took place in several parts of the country, with the Reuters news agency reporting at least 14 people died in the clashes.
In Cairo's packed Tahrir Square on Wednesday, anti-government protestors welcomed the military intervention with fireworks.
A 19-year-old female college student expressed her faith in the military, saying Morsi was as much a dictator as his predecessor Mubarak.
Among Morsi supporters who gathered in a suburb of Cairo, a 35-year-old man said Morsi's rule was democratically mandated and that a coup d'etat will only divide the people further.
Meanwhile, U.N. Secretary General Ban Ki Moon expressed concern over the developments and sought a resolution through nonviolence and dialogue.
Without explicitly condemning the military, appealing Wednesday for calm, Ban said military interference in the affairs of any state is concerning, urging a swift reinforcement of civilian governance in accordance with democratic principles.
U.S. President Barack Obama also expressed concern over the situation, saying the United States would review its substantial military aid package to the country, estimated by the Associated Press as worth $1.5 billion annually.
If Washington officially declares the situation a coup d'etat, its laws require it to freeze the flow of aid.