Some 64 per cent of voters backed the charter over the two rounds of polling, state-run media reported. The final results of the referendum, however, are not expected until tomorrow.
With this, the grouping of Islamists and ultra-radical Salafists, who have won every election since the ouster of long-time ruler Hosni Mubarak in February 2011, appeared to have once again outmuscled the largely secular opposition, which claims abuses in voting.
An official of the Brotherhood's political wing Freedom and Justice Party claimed over 71 per cent of the voters cast a "Yes" ballot for the charter yesterday in second and final round of voting.
"According to our calculations, the final result of the second round is 71 per cent voting 'Yes' and the overall result (of the two rounds) is 63.8 per cent," he said.
The "Yes" vote won in the first phase on December 15 by a relatively narrow 56.5 per cent.
The draft constitution has caused serious divisions in Egypt as it was drafted by an Islamist-dominated assembly from which representatives of the church and liberals withdrew.
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The second round of voting yesterday in 17 governorates which hold half of Egypt's electorate held amid allegations of irregularities. Ten governorates voted during the first phase.
The opposition said violations like polling stations opening late and Islamists seeking to influence voters took place in the second round of referendum. (More)