Egyptians took to the polls Saturday to give their thumbs-up or thumbs-down to a controversial draft constitution that has had opposition protesters up in arms and on the streets for weeks.

The path to the referendum has been marred by violent incidents on both sides as well as extensive institutional and political power struggles, and President Mohamed Morsy and his allies have rushed the document to a popular vote.

Morsy, who himself has been the object of raucous mass opposition protests as well as mass demonstrations of support, cast his ballot early Saturday in the Cairo suburb of Heliopolis, according to state-run news agency MENA.

Sentiments about the national charter have been split down the same political lines of those who support the president and those who oppose him and have been equally as heated.

Those opposed to it feel it contains subtle wording that limits rights and gives too much political power to religious figures and institutions.

Many in the opposition called earlier for a boycott of the referendum, but most have swung around to urging citizens to turn out and vote "no."

Liberal oppositionist Mohamed ElBaradei -- better known globally than in his native Egypt due to his former role as head of the International Atomic Energy Agency -- is one of them.

"To every Egyptian -- male and female: Listen to the voice of reason and conscience. Vote 'no' in order to save Egypt and support the nation," he tweeted Saturday morning in Arabic to fellow Egyptians.

He later tweeted in English, "Adoption of divisive draft constitution that violates universal values & freedoms is a sure way to institutionalize instability & turmoil."

Former presidential candidate and prominent opposition leader Hamdeen Sabahy called for a "no" from his followers in a tweet Saturday: "We deserve a constitution that is worthy of the revolution and the dignity of its martyrs."

Supporters of the draft constitution herald what they say is its protection of personal rights, especially its provisions on handling of detainees in the judicial system, which made capricious use of its powers under deposed autocratic president Hosni Mubarak.

Dr. Esam al-Erian, Morsy's adviser and deputy head of the Islamist Freedom and Justice Party said on his party's Facebook page: "Holding the referendum marks a new phase in Egypt's history. It ends hopes of those wishing for Mubarak's return."

Hassan el-Shafie, a senior cleric and member of the Constituent Assembly that drafted the constitution, called opposition to the document "purely political," saying the highest Islamic institution in the land "has made it ultimately clear that the country must be a modern democratic nation."

International rights group Human Rights Watch says the draft constitution "protects some rights but undermines others." It "fails to end military trials of civilians or to protect freedom of expression and religion," it said in a statement.

Egypt's Christian leaders have neither come out for or against the constitution, but instead encouraged believers to vote their own conscience.

Though election observers are officially allowed, rights organizations have criticized the lack of real monitoring possibilities, and well-known international observer teams have not announced their participation.

A group of 21 Egyptian human rights organizations accused the government body responsible for monitoring of bias and manipulation in a statement released Thursday.

"Currently, the NCHR (National Council for Human Rights) is attempting to monopolize civil society's efforts to monitor the referendum, despite the fact that the council lacks impartiality," the group wrote. They accuse the body of being stacked with Mosry supporters who participated in drafting the constitution.

The Carter Center, which has sent 140 witnesses to observe Egyptian elections in the past, declined to send a delegation to observe the referendum.

"The late release of regulations for accreditation of witnesses precludes the Center from conducting a comprehensive assessment of all aspects of the referendum process, consistent with its methodology for professional observation of elections," the center said in a statement Thursday.