Cairo - Egyptians voted in favour of a constitution shaped by Islamists but opposed by other groups who fear it will divide the Arab world's biggest nation, officials in rival camps said on Sunday after the first round of a two-stage referendum.
Next week's second round is likely to give another "yes" vote as it includes districts seen as more sympathetic towards Islamists, analysts say, meaning the constitution would be approved.
But the narrow win so far gives Islamist President Mohammed Morsi only limited grounds for celebration by showing the wide rifts in a country where he needs to build a consensus for tough economic reforms.
The Muslim Brotherhood's party, which propelled Morsi to office in a June election, said 56.5% backed the text. Official results are not expected until after the next round.
While an opposition official conceded the "yes" camp appeared to have won the first round, the opposition National Salvation Front said in a statement that voting abuses meant a rerun was needed - although it did not explicitly challenge the Brotherhood's vote tally.
Rights groups reported abuses such as polling stations opening late, officials telling people how to vote and bribery. They also criticised widespread religious campaigning which portrayed "no" voters as heretics.
A joint statement by seven human rights groups urged the referendum's organisers "to avoid these mistakes in the second stage of the referendum and to restage the first phase again".
Morsi and his backers say the constitution is vital to move Egypt's democratic transition forward. Opponents say the basic law is too Islamist and tramples on minority rights, including those of Christians who make up 10% of the population.
The build-up to Saturday's vote was marred by deadly protests. Demonstrations erupted when Morsi awarded himself extra powers on 22 November and then fast-tracked the constitution through an assembly dominated by his Islamist allies.