CAIRO (AFP) -- Western and Arab efforts to mediate an end to Egypt's political deadlock have failed, the presidency said Wednesday, signalling a possible crackdown on Islamists that has sparked fears of more carnage.
The statement came hours after US Deputy Secretary of State William Burns left Cairo, having made no headway in finding a compromise between the army-installed government and supporters of deposed Islamist president Mohammed Morsi.
"The phase of diplomatic efforts has ended today," the presidency said, referring to mediation by Burns and EU envoy Bernardino Leon, who were among other diplomats who had travelled to Cairo.
"These efforts have not achieved the hoped for results," the statement added.
The statement suggested the government may now move against Cairo sit-ins by Morsi's supporters.
The presidency "holds the Muslim Brotherhood completely responsible for the failure of these efforts, and for consequent events and developments relating to violations of the law and endangering public safety."
More than 250 people have been killed in clashes since Morsi's ouster by the military on July 3, following days of mass rallies demanding the president's resignation.
The government had already tasked police with ending the sit-ins and Islamist protests, which it described as a "national security threat," but held off amid intense diplomatic efforts to find a peaceful resolution.
An airport official said Burns, in Cairo since Friday, left on Tuesday night after days of talks with the interim rulers and Morsi's Muslim Brotherhood.
Adding his weight to the drive for a peaceful resolution to the crisis, United Nations Secretary General Ban Ki-moon urged the release of Morsi, who has been formally remanded in custody in an undisclosed location.
He "reiterated his call for the release" of Morsi during a call with Egypt's Foreign Minister Nabil Fahmy, the UN said late Tuesday.
The government, which has faced intense domestic pressure to crack down on Morsi's supporters, lashed out on Tuesday against what it called excessive international pressure.
"Foreign pressure has exceeded international norms," the official MENA news agency quoted presidential spokesman Ahmed al-Muslimani as saying.
His statement came as US senators John McCain and Lindsey Graham outraged the government's supporters by describing Morsi's removal as a "coup," during a press conference in Cairo.
"The people who are in charge were not elected, and the people who were elected are now in jail," Graham said.
The comments drew a harsh rebuke from the presidency, which described the comments as "clumsy."
Graham and McCain were later asked by CBS News if they were alarmed by what is happening in Egypt.
"Oh my God," Graham responded. "I didn't know it was this bad. These people are just days or weeks away from all-out bloodshed."
Western envoys had pressured the Brotherhood to end its sit-ins, according to Islamists who attended the talks.
The diplomats had also demanded the government release jailed Islamist leaders as a confidence-building measure.
Morsi himself is being held on suspicion of having collaborated with Palestinian militants to kill policemen and stage jail breaks during an early 2011 uprising against strongman Hosni Mubarak, while Morsi was in prison.
The Brotherhood's supreme guide, Mohamed Badie, and his deputies will stand trial on charges of inciting the shootings of protesters outside their headquarters on June 30.
The government says it is up to the judiciary to release the prisoners, and it cannot intervene.
The Islamists say their release is a precondition for further talks on finding a settlement, which could include symbolically reinstating Morsi, who would then call for early elections.
With the failure of the talks, the government will now focus on ending the sit-ins in Cairo, which the presidency described as "terror originating spots."
Authorities have promised demonstrators a safe exit and said an end to their protests would allow the Brotherhood's return to political life.
Police say they have finished preparations for forcibly dispersing the sit-ins, where thousands have camped out in tents for more than a month.
More than 80 of the protesters were killed in clashes with police at the main sit-in outside Cairo's Rabaa al-Adawiya mosque on June 27.
Over 50 people died in earlier clashes with soldiers outside elite army headquarters.
