U.N. Secretary-General Ban Ki-moon said on Monday he was "deeply disturbed" by the deaths in custody of 37 supporters of the Muslim Brotherhood in Egypt and condemned an ambush by Islamist militants that killed 25 Egyptian policeman.
The Muslim Brotherhood supporters died on Sunday while being transferred to a prison. Government officials said they were suffocated by tear gas during an attempted escape, but the Brotherhood said the men were murdered and demanded an inquiry.
"The Secretary-General calls for a full investigation to ascertain the facts surrounding this incident," Ban's press office said in a statement.
The Egyptian policemen were on their way to their barracks in Rafah, near the border with Israel, when militants attacked them with machine-guns and rocket-propelled grenades on Monday, according to security sources.
Almost 900 people, including more than 100 soldiers and police, have been killed since the authorities forcibly dispersed Muslim Brotherhood sit-ins in Cairo on Wednesday.
"With such sharp polarization in Egyptian society, both the authorities and the political leaders share the responsibility for ending the current violence. They should spare no effort to swiftly adopt a credible plan to contain the violence and revive the political process," Ban told a news conference.
He said "the political space for the Muslim Brotherhood should be expanded, because their political space has been very limited."
He also said Egypt's democratically elected President Mohamed Mursi - who was removed from power by the army and detained on July 3 after massive protests against him - should be freed or subjected to a transparent legal process.
Ban said U.N. political affairs chief Jeffrey Feltman would hold discussions this week in Cairo "with a focus on how the United Nations can best support initiatives to restore peace and forge reconciliation in Egypt."