Egypt's interior ministry on Thursday promised ousted president Mohamed Morsi's supporters "safe exit" if they quickly leave their Cairo protest camps as police prepared to disperse them amid international appeals for restraint.
The call to disperse, which came after police commanders discussed how to carry out orders from the military-installed interim government to end the protests, was immediately rejected by the demonstrators.
Diplomatic efforts to avoid further bloodshed picked up pace, with EU Middle East envoy Bernardino Leon and German Foreign Minister Guido Westerwelle both arriving in Cairo to urge the rival camps to find common ground.
The United States was also working with the European Union to resolve the crisis, Secretary of State John Kerry said in an interview in Pakistan.
Kerry said the military's removal on July 3 of Islamist president Mohamed Morsi-- the country's first democratically elected president -- had come at the request of millions, but he warned against further bloodshed.
"The military was asked to intervene by millions and millions of people, all of whom were afraid of a descendance into chaos, into violence," Kerry said, in comments that will be seen in Egypt as supportive of the interim rulers.
"And the military did not take over, to the best of our judgement - so far. To run the country, there's a civilian government. In effect, they were restoring democracy," he added.
The interior ministry's warning came as police prepared to disperse thousands of pro-Morsi protesters, raising fears of more violence.
The ministry had already warned that the demonstrations would be dispersed "soon," but without saying when or how.
A senior member of the Freedom and Justice Party, the political arm of Morsi's Muslim Brotherhood, said the European envoys asked them to end their sit-ins.
"All the European delegates have the same message; they are pressuring the anti-coup protesters to disperse the sit-ins," said the official.
The interior ministry statement called "on those in Rabaa al-Adawiya and Nahda squares to let reason and the national interest prevail, and to quickly leave."
The ministry "pledges a safe exit and full protection to whoever responds to this appeal," the statement added.
Following a meeting with Muslim Brotherhood representatives, Westerwelle warned that the situation was "very explosive."
"We have seriously and adamantly pressured for a peaceful solution. I hope that those concerned have gotten the message," he said in a statement.
"The international community has to keep up its diplomatic efforts, even though we don't know today whether these will prove successful."
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Kerry, in his interview with the Pakistani Geo television, warned against further bloodshed.
The United States was "very, very concerned" about the killing of dozens of pro-Morsi protesters in clashes with security forces , warning that it is "absolutely unacceptable."
Allaa Mostafa, a spokeswoman for the pro-Morsi Anti Coup Alliance, told AFP the protesters would continue their sit-ins.
Ministers had ordered police to end sit-ins and marches by Morsi's Islamist supporters, saying they amounted to a "national security threat."
The orders raised fears of new violence, less than a week after 82 people were killed in clashes at a pro-Morsi rally in Cairo.
EU envoy Leon also landed in Cairo on Wednesday, to follow up on three days of intensive diplomacy by the bloc's foreign policy chief, Catherine Ashton.
British Foreign Secretary William Hague called for "an urgent end to the current bloodshed" and the release of Morsi, in a phone call to interim vice president Mohamed ElBaradei, the Foreign Office said.
And Amnesty International condemned the cabinet order as a "recipe for further bloodshed."
In Rabaa al-Adawiya, the mood was calm after the cabinet's announcement. Thousands of protesters have been camped out in a tent city at the square.
Foreign trade minister Munir Fakhry Abdel Nur said Wednesday's statement did not "give room for interpretation."
Accusing Morsi supporters of bearing arms, he told AFP: "It is clear the interior ministry has been given the green light to take the necessary measures within legal bounds."
The interim government also faces an increase in militant attacks in the restive Sinai peninsula, where gunmen on Thursday shot dead a policeman in the northern town of El-Arish, security officials said.
Much of the Egyptian media expressed support for the government's decision, with some saying the interim administration had received "the people's mandate" in demonstrations last Friday backing Morsi's overthrow.
More than 250 people have been killed since the president ouster following nationwide protests against his single year in power.
Further raising tensions on Wednesday, judicial sources said three top Brotherhood leaders, including Supreme Guide Mohamed Badie, would be referred to trial for incitement to murder.
Morsi himself has been formally remanded in custody on suspicion of offences when he broke out of prison during the 2011 revolt that toppled president Hosni Mubarak.
He was detained hours after the coup and is being held at an undisclosed location, where the EU foreign policy chief met him on Tuesday, later telling reporters he was "well."