Supporters of deposed Islamist president Mohamed Morsi manned makeshift barriers as they braced for a crackdown as early as Monday on their Cairo protest camps following the expiry of a government ultimatum.
Morsi loyalists, led by his Muslim Brotherhood movement, have kept in place two huge protest camps in the capital and have also staged almost daily demonstrations around Egypt against the Islamist leader's July 3 ouster by the military.
The country's army-installed interim leaders have repeatedly warned them to leave, even promising the Brotherhood a return to political life for an end to the protests.
With over 250 people killed since Morsi was overthrown and detained, authorities say they are eager to avoid more bloodshed.
The dispersal of the sit-ins will be "gradual", with protesters given "several warnings" before police move in, senior security officials told AFP.
"There will be a series of gradual steps. We will announce every step along the way," an interior ministry general told AFP.
Once the siege begins, the protesters will be "surrounded", no one will be let into the sit-ins and the protesters will be given several warnings to leave, another security official said.
"This will last two to three days," he said.
At the main Rabaa al-Adawiya sit-in, dozens of men wearing helmets and holding clubs on Monday guarded makeshift brickwall barriers.
Those in the camp insisted they were not scared of the looming crackdown.
It's Muslim "doctrine that there is nothing worse than turning your back," one protester told AFP.
Others acknowledged that police will eventually break through if they want.
"We will have martyrs. It will be a high price to pay, but there will be victory in the long run," another said.
Al-Azhar, Sunni Islam's highest seat of learning, meanwhile, announced a last-ditch effort to resolve the tense political standoff and called for reconciliation talks between the rivals.
But Morsi loyalists defiantly called for new massive protests on Tuesday after again rallying to demand his reinstatement and condemn the army.
Senior Muslim Brotherhood official, Farid Ismail, told a news conference: "We want to send a message to the coup leaders: the Egyptian people insists on continuing its revolution ... And the people will insist on turning out in all squares."
"Sisi is a traitor, Sisi is a killer," shouted protesters who took part in a march Sunday of hundreds of women in central Cairo, referring to army chief Abdel Fattah al-Sisi who was behind Morsi's overthrow.
In east Cairo, a convoy of cars plastered with pictures of Morsi Sunday flooded the streets of a neighbourhood, with drivers blaring their car horns in a show of support for the deposed president.
Al-Azhar's Grand Imam Ahmed al-Tayyeb is on Monday to launch contacts with political factions and hopes to organise reconciliation talks later this week, state media reported.
"Al-Azhar has been studying all the proposals for reconciliation put forward by political and intellectual figures... to come up with a compromise formula for all Egyptians," Tayyeb's adviser, Mahmud Azab, told state-owned daily Al-Ahram.
But the Muslim Brotherhood is likely to reject an invitation for dialogue with Tayyeb as he had sat alongside Sisi when the army chief announced the Islamist president's overthrow.
The interim leadership has drawn up a political roadmap for Egypt's transition which provides for new elections in 2014, and it has said the Brotherhood can take part in the transition.
More than 250 people have been killed in clashes since Morsi's ouster, following several mass rallies demanding his resignation.
A demonstrator at one sit-in said: "We are protesting because they have thrown our votes into the rubbish bin. Morsi was elected democratically and nothing can replace democracy."
Morsi's turbulent single year in power polarised Egyptians and his ouster has deepened divisions.
His critics say he concentrated power in Brotherhood hands and that under his tenure political divisions spilled out onto the streets in deadly clashes while the economy tumbled.
On June 30, millions took to the streets to demand Morsi's ouster, openly calling on the army to remove him.
The interim leadership is under heavy pressure at home to crack down on the pro-Morsi protests, and it has been pressed by the international community to avoid bloodshed.
Senior US, EU and Arab envoys have taken turns to fly into Cairo to try to persuade the two sides to find a peaceful way out of the crisis, but they have all left empty-handed.