A leading opposition figure warned of more blood on the streets when Egyptians vote on a new constitution championed by Islamist President Mohamed Mursi amid a growing political crisis.
In the referendum this Saturday and next, Egyptians must accept or reject a basic law that has to be in place before national elections can be held early next year - an event many hope can steer the Arab world's most populous nation out of its turmoil.
At least seven people have died and hundreds have been injured in violence that erupted three weeks ago after Mursi awarded himself sweeping powers to ram the charter through a drafting body dominated by Islamists and boycotted by the opposition.
Ahmed Said, a leading member of the opposition National Salvation Front, said pushing through the referendum with tension running high on the streets could provoke more violence as rival voters go to the polls.
"During the referendum, I believe there will be blood and a lot of antagonism, so it is not right to hold a referendum," he told Reuters. Said, who also heads the liberal Free Egyptians Party, described the vote as too much of a risk with so much "bitterness" prevailing.
Despite a push for a "no" vote from the opposition, the measure is widely expected to pass given the well-organized Muslim Brotherhood's record of winning elections since the fall of Hosni Mubarak almost two years ago. Many Egyptians, tired of turmoil, may simply fall in line.
But the divisive referendum risks damaging Mursi's ability to forge a consensus on vital policies to save the economy. It may also fragment an opposition whose present unity may struggle to survive a decisive defeat at the ballot box.
The vote has proved hugely controversial, with supporters of the Islamist Muslim Brotherhood fighting in Cairo and other cities with members of the liberal, secular opposition.
The presidential palace, focus of mass street rallies, is ringed by tanks and huge concrete barricades.
State television showed on Thursday troops on parade being given orders to protect polling stations and other government buildings.
The opposition says the constitution does not reflect the aspirations of all 83 million Egyptians because it is too Islamist and tramples on minority rights, including those of the Christian community. Mursi's supporters say the constitution is needed to continue the transition to democracy.
This week the opposition staged a major push on the streets to persuade Mursi to postpone the referendum, without success. It was matched by even bigger Islamist demonstrations supporting the vote.
The opposition is now telling its supporters to vote "no". although it has threatened to boycott proceedings if certain guarantees for a fair vote are not met. But staying away from the process could risk a loss of credibility, political experts say.
For the opposition, the margin of any victory may be crucial.
"There is a real chance the result could demoralize the opposition, if the constitution is able to get 70 percent (support) or higher, it might be difficult to recover from that and Mursi is going to claim vindication," said Shadi Hamid of the Brookings Doha Center.
A senior member of the Muslim Brotherhood said a vote for the constitution would have practical political benefits for all Egyptians as it would shift legislative power, currently in the hands of the president, to an elected upper house of parliament.
"Say 'yes' for a better future, and distribute power between the institutions so they are not concentrated in one hand," said the Brotherhood's Essam el-Erian.
It is a message that might resonate with ordinary Egyptians weary of instability and economic uncertainty.
"Do I like the constitution?" asked Ahmed Helmy, a 35-year-old engineer in Cairo's Tahrir Square. "No, the panel that drafted it was a monopoly. But I want the referendum to take place so we can get out of this prolonged transitional period that's making me and millions of Egyptians wish they had left the country."
The economy is feeling the strain as rival factions clash on the streets. The Egyptian pound is hitting new eight-year lows against the dollar almost daily and a $4.8 billion loan from the International Monetary Fund seen as vital for a recovery has been put back to next month due to the crisis.
The United States is looking nervously at a country which it has supplied with billions of dollars in aid and whose regional importance is underlined by a peace treaty with Israel.
The recipients of much of that U.S. aid, the Egyptian military, have held back from the kind of political role they relished under Mubarak and his predecessors. An invitation by the head of the army to hold national unity talks this week was cancelled when the effort was seen as too politicized.
With street protests reducing debate to little more than exchanges of slogans, campaigning has got off to a slow start.
Some opposition activists have called for a rally on Friday in Tahrir Square, the cauldron of the anti-Mubarak revolt. For their part, Muslim Brotherhood members are distributing free copies of the constitution.
Broadcast media have offered voters guidance on how the referendum will be run, telling them they must dip a finger in ink once they have cast their ballots to avoid multiple voting.