Supporters of ousted Egyptian president Mohamed Morsi rallied on Sunday to demand his reinstatement, even as officials said a "gradual" break-up of their protest camps was imminent, AFP reports.
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 rival sides.
Before the police finally moves in, Morsi loyalists are to be given fresh warnings to evacuate the two protest camps erected in Cairo since the army ousted the Islamist leader on July 3, security officials told AFP.
They did not give a date for the launch of operations but the interim government has repeatedly warned the camps will be dismantled after the Muslim holidays of Eid al-Fitr which came to a close on Sunday.
Defiant Morsi loyalists called for new massive protests on Tuesday after again rallying to demand his reinstatement and condemn the army.
"Sisi is a traitor, Sisi is a killer," shouted protesters who took part in a march 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 flooded the streets of a neighbourhood, with drivers blaring their car horns in a show of support for the deposed president.
Morsi loyalists, led by his Muslim Brotherhood movement, have kept in place the huge protest camps in the capital and have also staged almost daily demonstrations around the country.
They insist they will empty the camps, where women and children figure among the protesters, only if he is reinstated.
But the interim government, which took over just hours after Morsi's ouster more than a month ago, is determined to dismantle the protest sit-ins at Rabaa al-Adawiya and Nahda.
"There will be a series of gradual steps. We will announce every step along the way," an interior ministry general told AFP of measures to break up the Cairo sit-ins.
Once the siege begins, the protesters will be "surrounded" and will be given "several warnings" to leave, another security official said, adding that the operation will last "two to three days".
Both officials, who requested anonymity, did not specify when the operation will start, with one of them saying: "No final decision has been taken."
But a 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".
In a sign of the mounting tension, electricity briefly went out on Saturday night at Rabaa al-Adawiya, triggering panic among pro-Morsi protesters who thought the feared assault had begun.
Sunday's rallies -- which came after the Anti-Coup Alliance of Morsi supporters announced 10 marches around the capital -- came as Al-Azhar called for political reconciliation talks.
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.