William Hague has condemned Egyptian security forces for violent clashes which have left dozens of protesters dead.
The UK Foreign Secretary called on all sides to end the violence and warned leaders it was their responsibility to reduce tensions following some of the worst scenes since the 2011 uprising that overthrew president Hosni Mubarak.
Doctors at a local field hospital said 38 supporters of ousted president Mohammed Morsi were killed after police tried to disperse crowds when they tried to extend a long-running sitting in eastern Cairo, but warned the final death toll was likely to be far higher.
Anti-Morsi demonstrators also took to the streets yesterday following calls from military chiefs, with crowds gathering in Cairo's Tahrir Square.
Mr Hague said: "I am deeply concerned by recent events in Egypt, and condemn the use of force against protesters which has led to the loss of lives.
"I call on all sides to refrain from violence. Now is the time for dialogue, not confrontation. It is the responsibility of leaders on all sides to take steps to reduce tensions.
"I call on the Egyptian authorities to respect the right of peaceful protest, to cease the use of violence against protesters, including live fire, and to hold to account those responsible.
"I also call on the Egyptian authorities to release political leaders detained following the events of July 3, or charge them in accordance with the law. Such charges must be free from any suspicion that they are politically motivated.
"In our view, Egypt needs a political process that includes all groups on an equal footing leading to early and fair elections which all parties are able to contest."