Egypt's disputed Islamist-backed constitution passed with a 63.8 percent "yes" in a referendum, the election commission announced Tuesday, Dec 25, rejecting opposition allegations of significant vote fraud, The Associated Press reported.

Turnout of 32.9 percent of Egypt's nearly 52 million registered voters was quite a bit lower than most other elections since the uprising nearly two years ago that ousted authoritarian leader Hosni Mubarak.

This is the first constitution since Mubarak's ouster. The opposition had campaigned against it with massive street protests that sometimes turned deadly, arguing that it will usher in Islamic rule in Egypt and restrict freedoms. It has vowed to challenge the referendum results and fight for a share of power in the upcoming parliamentary vote expected within two months.

Judge Samir Abou el-Maati, the head of the electoral commission, denied allegations that judicial supervision was lacking in the vote. He said the total number of people who voted against the constitution was 6.06 million out of 16.7 million valid votes, or about 36.2 percent.

Opposition spokesman Khaled Dawoud said the judge didn't address complaints about overcrowding of polling stations. The opposition says the overcrowding was due to a boycott by some judges who traditionally oversee elections and that was a major factor in the low turnout.