Tens of thousands of protesters rallied in Cairo on Friday to pile pressure on President Mohamed Morsi after a panel dominated by fellow Islamists rushed through a controversial draft constitution.
The new charter, adopted after a marathon overnight session boycotted by liberals and Christians, raises serious human rights concerns, including about religious freedom, activists say.
Morsi will review the draft on Saturday, said assembly head Hossam el-Ghiriani, and is then expected to call for a popular referendum within two weeks.
The constitution has taken centre stage in the country's worst political crisis since Morsi's election in June, squaring largely Islamist forces against liberal opposition groups.
"Down with the constituent assembly," vast crowds armed with megaphones chanted as they filed into Tahrir Square, the epicentre of the uprising that overthrew Hosni Mubarak in early 2011.
Banners condemned "dictatorial Morsi" while protesters shouted "down with the rule of the Guide," a reference to the leader of the Muslim Brotherhood movement, through whose ranks Morsi rose before becoming president.
A spontaneous protest broke out as Morsi prayed in a Cairo mosque, after the preacher called on Muslims to support the president, but with no major incident.
Clashes broke out in the northern city of Alexandria between pro- and anti-Morsi demonstrators, a security source said, but there were no immediate reports of injuries.
Rallies are due to be held by both camps in Cairo on Saturday.
The current crisis was sparked when Morsi issued a decree on November 22 giving himself sweeping powers and placing his decisions beyond judicial review, provoking mass protests and a judges' strike.
His decree prevented the top legal body the Supreme Constitutional Court from potentially dissolving of the Islamist-run constituent assembly, in a ruling it was to make on Sunday on the body's legality.
The constituent assembly had drafted a charter to replace the one suspended after president Hosni Mubarak's ouster last year, but its finalisation was brought forward amid the commotion caused by Morsi's decree.
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A judicial strike called by the top Cassation Court and several other tribunals could place the imminent referendum on the charter in jeopardy, if judges who normally supervise elections refuse to grant it legitimacy.
Activists have lambasted the charter, saying it protects certain rights by undermines others.
"Rushing through a draft while serious concerns about key rights protections remain unaddressed will create huge problems," Human Rights Watch's Middle East director Joe Stork said in a statement.
Amnesty International said the draft "raises concerns about Egypt's commitment to human rights treaties," specifically ignoring "the rights of women (and) restricting freedom of expression in the name of religion."
It pointed to an article that guarantees freedom of worship for Islam, Christianity and Judaism but makes no mention of other religions, thus "potentially excluding... religious minorities such as Baha'is and Shiites."
The document retained a vague Mubarak-era article stating that "Islamic law" is the main source of legislation, but added that this was to be interpreted along the tenets of Sunni Islamic rulings, a clause churches have opposed.
The draft also bans "insulting humans," which activists say could censor political criticism of the president.
Top opposition leaders Mohamed ElBaradei, former Arab League chief Amr Moussa and Hamdin Sabhi slammed the charter and said they would participate in a sit-in in Tahrir Square until the all recent Islamist gains were reversed.
"The president and his constituent assembly are currently staging a coup against democracy," said ElBaradei on Twitter, having earlier predicted the charter's "fate will be the dustbin of history."
Several private newspapers announced that they would not appear on Tuesday to protest what they say is a lack of press guarantees in the charter.
Private television channels are expected to follow suit on Wednesday.
In an interview broadcast Thursday night, Morsi repeated that his new powers will expire once the constitution is ratified, a point which Islamist supporters have repeatedly made in favour of his decree last week.
A senior member of Morsi's Muslim Brotherhood, speaking on condition of anonymity, said the Islamists' end game was to put the referendum to vote to grant Morsi's decision democratic legitimacy.