Egypt has adopted a new, Islamist-backed constitution with nearly two-thirds support in a referendum preceded by weeks of sometimes bloody protests, official media said on Sunday.

The secular-leaning opposition, which has alleged fraud, was mulling its next move in its campaign against the text, which it says limits the freedoms of religious minorities and women. It was to hold a news conference later Sunday.

Official results are due on Monday after the second and final round of voting on Saturday.

Unofficial tallies given by state media and by President Mohamed Morsi's supporters in the Muslim Brotherhood said 64 percent of those who voted backed the constitution.

"The Egyptian people continue their march towards finalising the construction of a democratic modern state, after turning the page on oppression," the Brotherhood's political arm, the Freedom and Justice Party, said in a statement.

Approval of the constitution would trigger parliamentary elections in two months' time to replace an Islamist-dominated assembly that was dissolved by Egypt's constitutional court before Morsi's election in June.

In the meantime, all legislative business will be handled by the senate, also under the sway of Islamists. On Saturday, Morsi appointed 90 additional senators, including eight women and 12 Christians, to further "national dialogue," his spokesman said.

The main opposition group, the National Salvation Front, said it had seen fraud in both rounds of voting.

The Front had tried to scupper the poll with mass rallies before switching its focus to a last-minute campaign to vote down the charter.

The text was drafted by a panel dominated by the Muslim Brotherhood and ultra-orthodox Salafist groups. Christians and liberals boycotted the process in protest at changes they saw as weakening human rights, especially those of women.

Combined turnout from both rounds was 32 percent, according to the Muslim Brotherhood.

In Washington, the Republican chairwoman of the Foreign Affairs Committee in the US House of Representatives, Ileana Ros-Lehtinen, called the vote "a defeat for the Egyptian people."

"We cannot celebrate the trade of an authoritative regime for an Islamic dictatorship," she said.

Sunday editions of Egyptian newspapers reflected the divisions in the country.

"Egypt heads to stability," read the front-page headline in state-owned Al-Akhbar.

"Mass violations," the mass circulation independent daily Al-Masry al-Youm reported.

The head of the Brotherhood's FJP, Saad al-Katatni, offered an olive branch to other parties on Saturday, saying in a statement the party hopes "to turn over a new leaf" in the political confrontation.

Pre-referendum tensions over the vote were seen in Egypt's second city Alexandria on Friday, when 62 people were hurt as stone-throwing mobs torched vehicles.

On December 5, eight people were killed and hundreds more injured in clashes between rival demonstrators outside the presidential palace in Cairo.

Some 250,000 police and soldiers were deployed to provide security during the referendum. The army has also positioned tanks around the presidential palace since early this month.

Morsi's vice president, Mahmud Mekki, whose post is not mentioned in the new charter, announced on Saturday that he was resigning.

He said he had wanted to resign in November but stayed on to help manage the political crisis.

State television reported that Central Bank chief Faruq El-Okda had also resigned, but later cited a cabinet source as denying it.