CAIRO (AP) -- Former U.S. President Jimmy Carter's center said Thursday it will not deploy monitors for Egypt's constitutional referendum, amid deepening polarization over the process of adopting a document guiding how the country is to be governed following its 2011 revolution.

The center was the main international group monitoring earlier Egyptian votes, and its absence increases the likelihood that, if the constitution backed by President Mohammed Morsi and his Islamist allies passes, the rushed process leading to the Saturday referendum will further undermine the document's legitimacy.

It also comes as opposition and rights groups warn that the breakneck pace of organizing the vote and changes to the procedure for accrediting elections monitors may lead to fraud in the vote.

Egypt was plunged into political crisis three weeks ago when Morsi issued a decree giving himself near-absolute power. The president rescinded the decree in the face of broad criticism and huge street protests, but not before a panel charged with drawing up the country's constitution pushed through a draft in a marathon Dec. 1 overnight session and the president ordered a referendum two weeks later.

Morsi's supporters say the constitution will help end the political instability that has gripped Egypt since the March 2011 overthrow of autocratic leader Hosni Mubarak in a popular uprising. His opponents say minority concerns have been ignored and the constitution is full of obscurely worded clauses that could allow Islamists to restrict civil liberties.

Compounding the sense of crisis are huge rival protests that draw tens and sometimes hundreds of thousands. On Dec. 5 pro-Morsi supporters attacked an opposition sit-in outside the presidential palace, leading to street clashes in which at least 10 people were killed -- the worst political violence since Morsi was elected president. Both sides have planned new mass rallies on Friday.

On Thursday, Egypt's diplomatic missions around the world opened their doors for a second day to let a half million registered Egyptian expatriates vote. Turnout appeared low on the first day.

Amid rising tensions, the Carter Center -- which monitored Egypt's past parliamentary and presidential elections -- said that it would not be able to conduct "a comprehensive assessment of all aspects of the referendum process." It cited in a statement the government's late release of regulations for election monitoring.

The same day, 20 Egyptian rights groups issued a joint statement warning of possible election fraud, and expressing concern that a state-run human rights council has taken charge of issuing monitoring permits, in the past obtained directly from the elections committee.

"The undersigned organizations are deeply concerned about the potential of rigging during or after the referendum," said the statement.

The opposition was torn between whether to boycott the process or campaign for a "No" vote, but on Wednesday the umbrella National Salvation Front called on Egyptians to cast ballots against the document. Groups said Thursday they had produced videos against the constitution and one party said it will send loudspeaker trucks to tour Cairo urging a "No" vote.

The opposition has still left open the possibility of a boycott if judges and monitors are absent and if the state doesn't provide protection to polling stations.

Egypt's most prominent democracy advocate and opposition coalition leader Mohamed ElBaradei made an impassioned plea to Morsi to delay the vote to avoid the "specter of civil war."

In an emotional televised message, the Nobel laureate told the Islamist leader, "Fear God, Dr. Morsi and postpone the referendum," but also said called on voters to cast "No" ballots if the referendum went ahead as planned.

"Rejecting (the draft) will be rejecting the policies that led to this draft," he said. "This referendum is void and the draft is void," he said.

A day earlier, ElBaradei tweeted that "insistence on a referendum in an explosive, polarized, chaotic and lawless environment is leading country to the brink."

The polarization has hit government bodies and other state institutions, in particular the judiciary.

On Thursday, the Judges' Club -- a body that acts as a union for judges -- held an emergency meeting denouncing the prosecutor general Talaat Abdullah for transferring an investigative judge who released anti-Morsi protesters detained at the palace clashes. The judge was since reinstated.

Prosecutor general Abdullah is a focus of judicial anger, as he was appointed and his predecessor removed as part of Morsi's special decree, even though the president normally does not have the power to fire prosecutors.

Prosecutors threatened to go on strike starting Monday if the prosecutor general does not step down, along with the Minister of Justice.

Morsi's decree prompted many judges to go on strike, and most will refrain from overseeing the constitution referendum, according to the Judges' Club. Egyptian elections law requires judicial oversight of the voting process.

Morsi has responded to the shortage of judges by breaking the vote into two rounds -- one on Saturday and another on Dec. 22. The country's Election Committee says there are 7,000 judges ready to oversee the first round of voting, which will include the provinces of Cairo and Alexandria, the country's two largest. He had said earlier that 9,000 judges were available.

The fracas over the constitution and the violence has fed into wider fears among many Egyptians that the Muslim Brotherhood aspires to monopolize power, after 80 years facing frequent bouts of repression and imprisonment by mostly military-backed, secular-leaning rulers.

Opponents of Morsi fear last week's violence outside the presidential palace was a signal that the Brotherhood will use force to push its agenda.

But the Brothers deny using violence and say they are usually on the receiving end, claiming that they suffered the majority of deaths during the palace fighting. Over the past three weeks, offices of the Brotherhood's Freedom and Justice have been torched by protesters in several cities around the country.

Late Thursday, a movie director who joined anti-Morsi demonstrations told the private Al-Nahar TV channel that he came under attack by Islamist protesters holding a sit-in for days in front of a media production facility outside Cairo. Khaled Youssef said he filed lawsuits against Islamist leaders for allegedly goading their followers to attack him.

Ultraconservative Islamists and Muslim Brothers have protested outside Media City, angry at what they say is biased coverage by private sector channels. Pro-Morsi protesters are also holding sit-ins outside the Supreme Constitutional Court while anti-Morsi protesters are holding sit-ins in downtown's Tahrir Square and in front of the presidential palace.

Earlier Thursday, clashes erupted inside Cairo's Ain Shams university after anti-Morsi students smashed windows and broke into a conference where a speaker invited by the Muslim Brotherhood was discussing the draft constitution.

University security guards smuggled the speaker, Islamist politician Mohammed Salim al-Awaa, out unharmed, according to a security official who spoke on condition of anonymity because he was not authorized to speak to the press.

The Brotherhood accuses former Mubarak supporters of paying thugs in an organized campaign to topple Islamists from power.

In his weekly message emailed to reporters, the group's top leader Mohammed Badie accused the opposition of practicing "the dictatorship of the minority."

But he also said the "honest opposition" was infiltrated by Mubarak supporters who are "cheating them with sweet words" and money. "There are hidden hands working at night trying to topple what is being built of elected institutions," Badie said.

Mubarak-era officials had also blamed "hidden hands" for stirring unrest.

An official in the president's office meanwhile said Thursday that Morsi plans to appoint 90 new members to the upper house of parliament. The lower house was dissolved in May by court order.

The new constitution stipulates that the largely powerless upper house will be given full legislative authority until a new lower house is elected. Islamists already occupy 80 percent of the 270-member Shura Council's seats. Turnout for the vote was less than 10 percent.

The official spoke on condition of anonymity because he was not authorized to speak to the press.