Four people have been killed in Egypt as supporters of ousted President Mohammed Morsi clashed with opponents and security forces.
Medical officials said at least 40 others were hurt as gunfire and explosions rocked the centre of Cairo.
The square has since been sealed off to prevent pro-Morsi supporters occupying the symbolic heart of the 2011 uprising which ousted Hosni Mubarak.
Troops used tear gas and live rounds to halt crowds heading to Tahrir Square.
Reports said the four fatalities were all Brotherhood supporters who died amid fighting in two Cairo neighbourhoods.
As clashes broke out in the capital, state TV reported further violence in the northern Sharqiya district and to the east in Giza, as well as in the northern port city of Alexandria.
There were also reports of skirmishes between pro-Morsi demonstrators and civilian supporters of the military government.
Early curfew
The BBC|s correspondent in Cairo, Quentin Sommerville, said that by early evening all was quiet on the streets of Cairo, ahead of the early Friday curfew at 1900 local time (1700 GMT).
A heavy security presence remained, he said.
Hundreds of Islamist protesters have died in violence since the Egyptian military deposed Mr Morsi in July, 13 months after he was elected as president.
Several senior figures, including Mr Morsi and the movement|s general guide Mohammed Badie, are being held on charges such as incitement to violence and murder.
Thousands of members of the Muslim Brotherhood have also been detained over the past two months.
Egyptian authorities portray the crackdown as a struggle against "terrorism". They are preparing to seize Muslim Brotherhood assets after appeal courts upheld a recent ban on its activities.
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