Details added (first version posted at 22:34)
Egypt's new constitution, favoured by supporters of Islamist President Mohammed Morsi, was approved by 63.8 per cent of voters in a two-round referendum, officials said Tuesday, dpa reported.
The charter, drafted by an Islamist-dominated assembly, was criticized by opposition groups who said it could undermine political rights and sideline minorities.
Morsi's Muslim Brotherhood and its conservative allies say the constitution will fast-track the country's transition to democracy from the authoritarian rule of president Hosny Mubarak, who was deposed almost two years ago.
About 33 per cent of the 51.9 million registered voters turned out for the December 15-22 ballot. The low turnout was expected to embolden the largely secular opposition, who announced they were getting ready for elections to the lower house of parliament, scheduled to take place within 60 days.
The Islamist-dominated Shura Council, or upper house, would be given the authority to legislate until a new legislature is elected.
Election commission chief Samir Abul-Maati rejected allegations by the opposition that the vote was marred by fraud and violations, including the lack of judicial supervision.
"We did not find any polling stations without judges as complaints said," Abdul-Maati said, adding that all complaints were investigated.
Many judges had announced they would not oversee the polls because of their stand-off with Morsi. They accused him of undermining judicial independence when he issued a decree in November making his decisions immune to judicial review.
Although the decree was cancelled, the judges held on to their position to boycott the polls because of a sit-in by Morsi's supporters around the Supreme Constitutional Court, which prevented the judges from resuming their work.
The election commission cancelled the results of some polling stations that were closed before the scheduled time.
The opposition April 6 movement slammed the vote. "The constitution lacks popular legitimacy," the group said, citing low turnout and violations reported by several monitors.
The draft constitution has polarized the country. Opposition leaders have warned of a possible civil war after backers and opponents of the charter fought street battles in which at least nine people died.