Foreign Secretary William Hague has appealed for “calm and restraint” in Egypt following clashes which have left at least 40 dead.
Violence flared outside a military building in Cairo where supporters of the former president Mohammed Morsi were holding a sit-in.
Mr Hague called for a full investigation into the incident and called for a "swift return to democratic processes" following the military intervention which ousted Mr Morsi.
The Foreign Secretary said: "I condemn the violence that led to the deaths of over 40 people during demonstrations in Egypt overnight. There is an urgent need for calm and restraint.
"I urge all sides to avoid violence and ensure all protests remain peaceful. I call on the Egyptian authorities to investigate the events that led to these deaths and ensure that those responsible are held to account in accordance with the rule of law.
"It is crucial that there is a swift return to democratic processes in Egypt. All sides of the political spectrum should work together for the sake of the country's political and economic future.
"It is for the Egyptian people to chart a way forward. However in our view this should include a path to free and fair elections in which all parties can compete, the release of political leaders and journalists, and work to agree a constitution and the checks and balances of a democratic system that respects the rights of all Egypt's citizens. Urgent steps to improve economic conditions in the country are also vital.
"As a friend, the UK stands ready to continue to support the people in their desire for a better Egypt."
The military deposed the democratically elected Mr Morsi In response to days of protests about his presidency and swore in senior judge Adly Mansour as interim leader.
Mr Morsi described last week's events as a "full coup" and his Muslim Brotherhood supporters have been holding rallies and a sit-in outside the Republican Guard building since he was ousted.
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