Supporters of the deposed President Mohamed Morsi continued to rally after an apparent call by Egypt's army chief to crack down on dissenters.
Thousands of pro-Morsi supporters filled Nasr City on Thursday, repeating their weeks-long demand that the deposed president - who was removed by the army on July 3 - is reinstated.
Military helicopters circled above Cairo early in the morning following a "state of alert" declaration by the army.
Egypt's interim Prime Minister Hazem el-Beblawi called for national reconciliation and said that all groups have the right to protest peacefully.
"Egypt is a civilian state, not a religious or military state," he said during a news conference. "I salute the call from the defence minister to the Egyptian people to express their right of speech."
Al Jazeera's Nadim Baba, reporting from Nasr City, said that the interim prime minister stressed on showing the world that Egypt is a secular country.
Following el-Beblawi's speech, Hesham Qandil, the deposed prime minister, proposed initiatives such as setting up a fact-finding commission and avoiding gatherings to "clear the atmosphere to move forward and engage in negotiations".
Many protesters have also gathered at the al-Azhar mosque, our correspondent said, as groups on both sides were calling for the continuation of demonstrations.
"Protesters here are calling for the Grand Imam of this mosque, Ahmed el-Tayeb, to go because he has accepted the roadmap for Egypt under interim President Adly Mansour," Baba said.
El-Beblawi's statement supported general Abdel Fattah El Sisi's comments on Wednesday who called for all Egyptians to rally against what he termed "violence and potential terrorism" on Friday.
In a speech to army graduates, he also denied accusations that he had betrayed the deposed president, Mohamed Morsi.
"I ask ... that next [upcoming] Friday all honest and trustworthy Egyptians must come out," Sisi said. "Why come out? They come out to give me the mandate and order that I confront violence and potential terrorism."
Elsewhere, Sisi vowed to stick to a political roadmap that laid the way for a reform of the constitution and new elections within some six months.
He said his appeal for protests was not a call for violence and expressed support for efforts for national reconciliation.
The military reacted soon after, declaring the "state of alert".
Ahmed Al-Meslemani, media adviser to the interim leader Mansour, echoed the call, asking people to take to the streets to protect the "revolutionary legitimacy" and support efforts to "fight terrorism".
The Muslim Brotherhood reacted quickly, with senior member Essam al-Erian issuing a statement directed at Sisi saying: "Your threat will not prevent millions to rally against [the] coup ... You have been always in your office conspiring."
Egypt's opposition Islamist coalition, led by the Muslim Brotherhood said Sisi should be tried by for crimes against humanity for calling for Friday's rally, which they said was "an announcement of civil war".
Our correspondent said that it was important that the interim prime minister backed Sisi's sentiments to calm those supporting the interim government who are unhappy that the general was "calling the shots".
Meanwhile, the Egyptian army said in a statement on Thursday, posted on a Facebook page affiliated to the military, that it would not "turn its guns against its people, but it will turn them against black violence and terrorism which has no religion or nation" after the protests planned for Friday.
'State of alert'
The state of alert includes additional army troops on streets in provinces in greater Cairo and surrounding areas.
Sources confirmed to Al Jazeera that armed forces would work on preventing attempts to "incite violence or terrorism".
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The army chief's speech came ahead of "national reconciliation" sessions called for by the interim leader Adly Mansour, and followed renewed violence in and outside the capital, in which at least three people died.
Both the Muslim Brotherhood and Al-Nour, Egypt's most powerful Salafi party, rejected invites to Mansour's first reconciliation sessions.
"For the Muslim, Brotherhood, the legitimate president of Egypt is Mohamed Morsi," our correspondent said.
Since Morsi's removal, over 100 people have been killed in violence, mostly during protests.