The United States and UN chief condemned clashes across Egypt on Friday and urged all leaders including the army to stop the violence after 37 people were killed following the toppling of president Mohamed Morsi.

"We condemn the violence that has taken place today in Egypt. We call on all Egyptian leaders to condemn the use of force and to prevent further violence among their supporters," State Department spokeswoman Jen Psaki said in a statement.

Tens of thousands of supporters of Morsi, who was deposed by the Egyptian military on Wednesday, protested across the country against his ouster.

"We expect the military to ensure that the rights of all Egyptians are protected, including the right to peaceful assembly, and we call on all who are protesting to do so peacefully," Psaki said.

"The Egyptian people must come together to resolve their differences peacefully, without recourse to violence or the use offorce"

Washington is increasingly caught in a dilemma, not wishing to condone what could be seen as a military coup, while recognizing that the democratically elected Morsi had failed to bring in an inclusive government.

Meanwhile, UN Secretary General Ban Ki-moon warned Egyptians against adopting "retribution tactics" in the country's worsening political crisis and called on security forces to prevent clashes, a spokesman said.

“Egypt's political leaders have a responsibility to signal, by their words and their actions, their commitment to a peaceful and democratic dialogue which includes all of Egypt's constituencies, including women," headded.