Supporters and opponents of deposed Egyptian president Mohamed Morsi on Saturday called for rival demonstrations on the 1973 Arab-Israeli war anniversary, after the deadliest violence in weeks killed four people.
Egypt's interior ministry warned it will "firmly confront" violence and protests that mar Sunday's 40th anniversary of the war as the authorities tightened security across the country, state media said.
The Anti-Coup Alliance of Islamist groups led by the Muslim Brotherhood called on its supporters to try to reach Cairo's Tahrir Square, blocked off by the army, to mark the war anniversary.
The conflict, known as the October war in the Arab world and the Yom Kippur war in Israel, is remembered proudly by the Egyptian army as it caught Israel's defences by surprise and led ultimately to Egypt's recovery of the Sinai Peninsula in a 1979 peace treaty.
"The Egypt Anti-Coup Alliance repeats its call to all Egyptians to continue their protests in every part of Egypt, and to gather in Tahrir Square on Sunday, October 6, to celebrate the army of that victory and its leaders," the bloc said.
Attempts on Friday by Islamist protesters against the army's July 3 overthrow of Morsi to reach Tahrir Square sparked clashes with security forces who responded with tear gas and warning shots.
Four people were killed in Cairo's deadliest violence in more than a month as demonstrators clashed with coup supporters as well as security forces.
It was unclear whether the dead were Islamists or their opponents. A senior medical official said only that none of them were security personnel.
Calls for demonstrations on Sunday were also made by Tamarod, the movement which led nationwide protests against Morsi that finally led to his ouster by the army and subsequent jailing.
"We call all Egyptians to come out tomorrow across all squares in the country to assert that this nation will not allow its revolution to be stolen," prominent Tamarod leader Mahmoud Badr told reporters.
Analysts said the Islamists' call for protests on Sunday marked a high-risk attempt to strip the current military high command of the army's legacy and patriotic pride in the Arab-Israeli conflict.
"They will try to show that the present army is not the army of all Egyptians, but only of those who backed the coup," said Hassan Nafaa, professor of political science at Cairo University.
"But this message will not go down well," he told AFP.
'There can't be another revolution'
Nafaa said the Islamists mistakenly believed they could repeat the 2011 protests that swept away veteran strongman Hosni Mubarak and his despised police.
"The Muslim Brotherhood fails to realise that there can't be another revolution," he said.
"Egyptian people are not against the army as they were against the police in January 2011. If there is violence tomorrow, the Muslim Brotherhood will be the loser."
The Anti-Coup Alliance said that Friday's bloodshed, which it blamed on "attacks on marches and protests," would only "increase our determination to continue the revolution".
But the authorities issued a warning to the Brotherhood.
"The interior ministry warns against attempts that may disturb the October 6 celebrations in Egypt," state news agency MENA quoted the ministry as saying.
"The ministry asserts its determination to firmly confront all violence and infringements of law by the Muslim Brotherhood supporters through their marches," it said.
The Anti-Coup Alliance has desperately sought to keep up the momentum of its protests against the military-installed interim government.
But its ability to mobilise large crowds has been sharply reduced by the rounding up of nearly all of its leaders.
More than 2,000 Islamists have been detained since security forces cleared two main Cairo protest camps on August 14 in an operation that left hundreds dead.
Top Brotherhood leaders are behind bars and face trial, including Morsi who is held at an unknown location since his ouster, while a court has banned the Islamist movement and seized its assets.
The United Nations, the United States and Germany voiced alarm at Friday's violence.
The protesters "have a responsibility to protest peacefully, to not incite violence, to not undertake violence of their own," said deputy US State Department spokeswoman Marie Harf.
In New York, UN chief Ban Ki-moon stressed "the importance of peaceful protest, respect for freedom of assembly and commitment to non-violence," his spokesman Martin Nesirky said.
German Foreign Minister Guido Westerwelle in a statement Saturday expressed concern over the new bloodshed in Egypt and urged leaders from both sides "not to pour oil on the fire".