Egypt's electoral commission has confirmed that a controversial, Islamist-backed constitution was passed by 64 per cent of voters, rejecting opposition allegations of polling fraud.
Those official results tallied with figures given by President Mohamed Morsi's Muslim Brotherhood immediately after the last round of polling at the weekend in the two-stage referendum.
The National Salvation Front opposition coalition, however, has already dismissed the plebiscite as "only one battle" and vowed to "continue the fight for the Egyptian people".
That sets the scene for continued instability after more than a month of protests, some of them violent, including clashes on December 5 that killed eight people and injured hundreds.
Many creditors, investors and tourists have abandoned Egypt because of the volatility that has prevailed ever since the early 2011 revolution that toppled veteran leader Hosni Mubarak.
The International Monetary Fund this month put on hold a $US4.8 billion ($A4.6 billion) loan the country needs to prevent a looming currency collapse.
The rating agency Standard and Poor's has downgraded Egypt's long-term credit rating one notch to B- because the "elevated" political tensions show no sign of abating.
Samir Abul Maati, the president of the national electoral commission, told a Cairo news conference late Tuesday that a total of 63.8 per cent of valid ballots supported the new constitution.
Turnout was 32.9 per cent, he said.
He added that opposition allegations of fake judges supervising some of the polling were unfounded.
The opposition, which has seized on the low turnout to challenge the legitimacy of the charter, appeared to be ready to accept the official results.
Front leader Mohamed ElBaradei, a Nobel Peace laureate and former chief of the UN atomic energy agency, admitted to the US network PBS on Monday that the referendum "is going to pass".
"But it's a really sad day in my view for Egypt, because it is going to institutionalise instability," he said.
ElBaradei said the new charter should be treated as "an interim one" until another is written up on the basis of consensus.
The opposition argues the Muslim Brotherhood and Salafist groups that backed the charter want to use some of its ambiguous language to slip in sharia-style strict Islamic law.
The text, which was written by a panel dominated by Islamists, has been criticised for weakening women's rights and other rights by the opposition and by the United Nation's human rights chief.
The Muslim Brotherhood counters that the constitution is a needed step to restoring stability.
The low turnout, though, confounded the Brotherhood's public predictions for the past month that voters would give greater support.
"Anything less than 70 per cent would not be good," Amr Darrag, a senior member of the Brotherhood's Freedom and Justice Party who helped draft the constitution, told AFP on December 2.
Attention is now turning to legislative elections that Egypt has to hold by the end of February. The previous parliament was dissolved in June by Egypt's constitutional court.
Morsi has ordered the Senate, which currently handles all legislative business, to convene on Wednesday, the official MENA news agency said.
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