The United States and the European Union have called on all sides in Egypt's political crisis to end "dangerous stalemate" after the interim government said foreign mediation had failed.
In a joint statement, they say the Egyptian government bears a special responsibility to begin this process.
More than 250 people have been killed in unrest since President Mohammed Morsi was ousted by the military on 3 July. Since then, diplomats from the US, the EU, Qatar and the United Arab Emirates have all tried to bring Egypt's political process back on track.
But on Wednesday the office of interim president Adly Mansour declared in a statement that the "phase of diplomatic efforts has ended today" and "These efforts have not achieved the hoped-for results".
The presidency says it holds the Muslim Brotherhood - which backs Mr Morsi - "completely responsible for the failure of these efforts", the BBC reports.
The statement came hours after US deputy secretary of state William Burns left Egypt following several days of talks. He was assisted by EU envoy Bernardino Leon. Shortly afterwards, US secretary of state John Kerry and EU high representative Catherine Ashton issued a joint statement.
"While further violent confrontations have thus far been avoided, we remain concerned and troubled that government and opposition leaders have not yet found a way to break a dangerous stalemate and agree to implement tangible confidence building measures," they say.
"This remains a very fragile situation, which holds not only the risk of more bloodshed and polarisation in Egypt, but also impedes the economic recovery which is so essential for Egypt's successful transition. Now is not the time to assess blame, but to take steps that can help initiate a dialogue and move the transition forward."
Cairo tense as Morsi supporters gather
Correspondents say Cairo is tense. Thousands of Mr Morsi's supporters outside the Rabaa al-Adawiya mosque in the suburb of Nasr City, and in Nahda Square, near the campus of Cairo University in Giza, have strengthened barricades in readiness for any action by security forces, witnesses say.
The interim government says it is determined to move against pro-Morsi protesters unless they voluntarily disperse.
Mr Morsi - Egypt's first democratically elected president - is under arrest at an undisclosed location. Several other senior figures from the Muslim Brotherhood have also been detained.
