CAIRO, Egypt -- Voters overwhelmingly supported Egypt's military-backed constitution in a two-day election, with 98.1 per cent supporting it in the first vote since a coup toppled the country's president, the election commission said Saturday.

The election was seen as key to legitimizing its military-backed interim government and wasn't a surprise, as authorities lobbied the public extensively to support it. But the turnout, only slightly higher than a referendum last year sponsored by the government of toppled Islamist President Mohammed Morsi, suggests a nation that is still deeply divided.

Egypt's High Election Commission said 38.6 per cent of the country's more than 53 million eligible voters took part in the two-day poll Tuesday and Wednesday. Judge Nabil Salib, who heads the commission, said 20.6 million voters cast ballots, with some 20.3 million votes counted after eliminating those voided.

Salib called the vote an "unrivalled success" and "an unprecedented turnout." However, a similar referendum in 2012 supported by Morsi's government saw a 32.9 per cent turnout.

This is the first vote since the military removed Morsi following massive protests in July. Officials view the vote as key in legitimizing the country's military-backed interim government and its plan for parliamentary and presidential elections.

Morsi's supporters and his outlawed Muslim Brotherhood group boycotted the vote and have alleged the results were forged. The Brotherhood has vowed to keep up their near-daily protests.

While announcing the results, Salib suggested voter participation would have been higher if it weren't for the vote coinciding with university midterm exams that kept students, and younger voters, away.

Activists and monitoring groups have raised serious concerns over the atmosphere in which voting took place, with U.S.-based Democracy International saying that "arrests and detention of dissenting voices" took place ahead of the poll.

"A democratic transition should be characterized by an expansion of freedoms, but Egyptians have seen substantial restrictions on the exercise of their democratic rights," said Eric Bjornlund, Democracy International's president and head of the observation mission in Egypt.

In the lead up to the vote, police arrested those campaigning for a "no" vote on the referendum, leaving little room for arguing against the document.

On Friday, supporters of Morsi took to the streets to denounce the draft charter. Some protests turned violent. Four people were killed in the ensuing clashes, Egypt's Health Ministry said Saturday. It said 15 people were injured nationwide.