The head of Egypt’s army has given a TV address, announcing that President Mohammed Morsi is no longer in office.
Gen Abdul Fattah al-Sisi said the constitution had been suspended and the chief justice of the constitutional court would take on Mr Morsi’s powers.
He said Mr Morsi had “failed to meet the demands of the Egyptian people”.
Later, the leader of the Muslim Brotherhood’s political wing, the Freedom and Justice party, and his deputy were detained, officials said.
Saad al-Katatni, who heads the party, and the Islamist movement’s deputy head, Rashad al-Bayoumi, were reportedly picked up hours after the speech.
Anti-Morsi protesters in Cairo gave a huge cheer in response to Gen Sisi’s speech.
However, US President Barack Obama said he was “deeply concerned” by the latest turn of events and called for a swift return to civilian government.