Thousands of people have gathered in Cairo to protest against a decision by the ruling military council to assume new powers.
The protests in Tahrir Square on Tuesday were called by the Muslim Brotherhood, which has said the army does not have the right to curb presidential powers following a vote the group says its candidate Mohammed Mursi won.
Official results from the weekend vote had not yet been announced, but Mr Mursi's rival, former Prime Minister Ahmed Shafiq, was also claiming victory.
As the vote was taking place the Supreme Council of the Armed Forces announced it was assuming legislative powers until a new parliament was elected.
Days earlier, it had implemented a court ruling to dissolve the Islamist-led parliament.
Activists have described the moves as a military coup.
However the BBC reports that there are plenty of Egyptians who seem to be reconciled to the prospect of the military continuing to exercise power, because they fear that otherwise the Muslim Brotherhood might turn their secular society into something resembling the theocracy of Iran.