Egypt's main opposition coalition, the National Salvation Front, has called for mass protests tomorrow to agitate against polling violations in the first round of the referendum on Saturday.
The National Salvation Front coalition said it would "not recognise any unofficial result," and would wait for the formal tally after next Saturday's second round of voting.
It called on Egyptians to "take to the streets on Tuesday to defend their freedoms, prevent fraud and reject the draft constitution."
It reiterated its allegation that balloting had been "marred by irregularities and violations".
The Muslim Brotherhood has said the group's tallies showed that 56.5 per cent of voters had supported the constitution, while 43 per cent had voted 'no' in first round of voting.
"Country split, flagrant irregularities, low turnout, disillusion with Islamists on the rise. Illiteracy remains a hurdle," Mohamed ElBaradei, head of the Front and former chief of the UN nuclear energy agency, said on Twitter.
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Preliminary results from the first phase of Egypt's constitutional referendum show there are increasing levels of division within society, ElBaradei said.
"Poverty and illiteracy provide fertile ground for trading with religion," ElBaradei added.
Several Egyptian human rights and monitoring groups claimed there were irregularities and demanded Saturday's vote be done over.
They alleged monitors were excluded from some polling stations, judges were not present in all as required and some fake judges were seen. Some also alleged that women were prevented in some cases from casting their ballot.
The electoral commission, "in the interest of national consensus", must "recognise that it was not capable (of ensuring) good organisation and it must redo the referendum," said Negad el-Borei, a spokesman for one of the groups, which represents lawyers.