Egypt’s Muslim Brotherhood is claiming that the country’s new draft constitution has been passed after the final round of voting in a referendum, even as the opposition has claimed the group engaged in voting fraud.

The Muslim Brotherhood, from which President Mohamed Morsi hails, and the official al-Ahram newspaper reported that about 64 percent of voters supported the constitution, after preliminary results were tallied from the second round on Saturday.

The early results are based on reports from returning officials from the vast majority of stations over the two rounds, which were held a week apart. Official results will be announced by the country’s election committee on Monday, pending appeals.

The National Salvation Front (NSF), Egypt’s main opposition coalition, has, however alleged that there had been incidents of fraud during the vote.

“We’re going to challenge this in the courts, we’re going to challenge this in the streets, we’re going to challenge this until we die, because we cannot recognise this wide attempt to steal the people’s future,” Ahmed Hawary, a spokesperson for the NSF, told Al Jazeera.

In a statement, the NSF said that it would be file documentation related to the fraud allegations with the country’s electoral commission before the announcement of final results.

Al Jazeera’s Rawya Rageh, reporting from Cairo, said that while the results were so far unofficial, the Muslim Brotherhood’s figures on elections have usually been close to accurate. She said that the low turnout figures, however, were of concern to both camps.

“Some 30 percent only of eligible voters turned out to vote in both rounds. once again raising questions of how the leadership of both the opposition and the Islamic camp have failed to appeal to the public and get them to vote in the first place,” she said.

The December 15 first round returned 57 percent in favour of the constitution, according to unofficial data. The vote was split over two days as many judges refused to supervise the ballot.

Backers of Morsi say the constitution is vital to move to democracy, nearly two years after a revolution that overthrew authoritarian ruler Hosni Mubarak. It will provide stability for a weak economy, they say.

But the opposition accuses Morsi of pushing through a text that they claim favours Islamists and ignores the rights of Christians, who make up about 10 percent of the population, as well as women.

Vice-president resigns

Meanwhile, Egypt’s vice-president announced his resignation even as voters were still going to the polls on Saturday, state TV reported.

Mahmoud Mekki’s resignation was announced just hours before the end of voting in the second and final round of the referendum on the constitution.

Fifty-eight-year-old Mekki, a career judge, said that he intended to quit once the charter was adopted. The new constitution eliminates the post of vice-president.

“I have realised a while ago that the nature of politics don’t suit my professional genesis as a judge,” he wrote.

Late on Saturday, Morsi announced the names of 90 new members he had appointed to the upper house of parliament, state media reported, and a presidential official said the list was mainly liberals and other non-Islamists.

The president’s main opponents from liberal, socialist and other parties said they had refused to take any seats.

Two-thirds of the 270-member upper house was elected in a vote early this year, with one third appointed by the president.

“What happens next is that when the official results are announced on Monday by the higher election commission, we’re expecting President Morsi to call for parliamentary elections in two months from now. And those parliamentary elections are going to be the next serious battle for both camps,” reported Al Jazerea’s Rageh.