Supporters of ousted Egyptian president Mohamed Morsi have pledged to defy a crackdown ordered by the army-installed interim government, as diplomats scrambled to broker an end to the crisis.
Morsi's Islamist backers said on Thursday they would hold a "march of the millions" on Friday, and denounced the orders given to police by the interim cabinet to end their Cairo sit-ins.
Diplomatic efforts picked up pace, with the EU's Middle East envoy and German Foreign Minister Guido Westerwelle both arriving in Cairo to urge the rival camps to avoid bloodshed and find common ground.
"The national alliance supporting legitimacy and defying the coup calls upon all the free people of the world to demonstrate peacefully in (an) 'Egypt against the coup' march of the millions," a coalition of Morsi loyalists said in a statement.
It denounced the government's call for its protests to be broken up and urged "all honourable military and police forces not to direct their bullets at their brothers and sisters of the Egyptian people".
The order from the government came on Wednesday afternoon, and raised fears of new violence, less than a week after 82 people were killed in clashes at a pro-Morsi rally in Cairo.
"The continuation of the dangerous situation in Rabaa al-Adawiya and Nahda squares, and consequent terrorism and road blockages, are no longer acceptable given the threat to national security," the cabinet said in a statement.
"The government has decided to take all necessary measures to confront and end these dangers, and tasks the interior minster to do all that is necessary in this regard, in accordance with the constitution and law."
The international community, which has expressed mounting concern over the violence since Morsi's July 3 ouster, warned against further bloodshed.
The US State Department called on the interim authorities to "respect the right of peaceful assemblies.
"That obviously includes sit-ins," spokeswoman Marie Harf told reporters.
British Foreign Secretary William Hague called for "an urgent end to the current bloodshed" and the release of Morsi, in a phone call to Egypt's interim vice president Mohamed ElBaradei, Britain's Foreign Office said.
Amnesty International condemned the cabinet order as a "recipe for further bloodshed".
Human Rights Watch took issue with the justification given by the interim authorities.
"A peaceful protest is NOT a 'national security threat'," tweeted its executive director, Kenneth Roth.
The German foreign minister, who arrived in Cairo on Wednesday, urged both sides to remain peaceful and seek an inclusive solution.
He was due to be joined by EU envoy Bernardino Leon, who was to follow up on three days of intensive diplomacy by the bloc's foreign policy chief, Catherine Ashton.
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.
The interior ministry had already warned that the demonstrations would be dispersed "soon", but without saying when or how.
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."
Much of the Egyptian media expressed support for the government's decision, with some stressing that 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 army ousted him following nationwide protests against his single year in power.
