(BBC NEWS) Cairo – Soldiers and police moved into Tahrir Square before dawn, using batons and tear gas to drive out the protesters, who retaliated by throwing stones.
By dawn, the demonstrators had returned to the square, while the troops again manned barricades in nearby streets.
The US secretary of state has said she is “deeply concerned” by the violence.
Hillary Clinton urged security forces “to respect and protect the universal rights of all Egyptians, including the rights to peaceful free expression and assembly”.
“Those who are protesting should do so peacefully and refrain from acts of violence,” Mrs Clinton added.
UN Secretary General Ban Ki-moon also said he was highly alarmed at the “excessive use of force employed by the security forces’, and called for the authorities to act with restraint and uphold human rights.