CAIRO — Tens of thousands of backers and foes of Egypt's Islamist president took to the streets in competing demonstrations Tuesday, as divisions over a draft constitution that is set for a referendum Saturday spilled into violence for the second time in two weeks.
Four opposition groups held marches and converged on the presidential palace, as Muslim Brotherhood offices were attacked across the country. The Islamists held countermarches after busing in thousands to a Cairo neighborhood that is considered a stronghold for the Muslim Brotherhood.
Other supporters camped outside independent media outlets critical of President Mohammed Morsi and threatened to storm their offices.
Egypt's military called on the Islamist-dominated government and the opposition — which includes liberals, secularists and Christians — to open a dialogue to resolve their differences.
Gen. Abdel Fattah el-Sissi, defense minister and chief of Egypt's armed forces, asked all political groups to meet Wednesday at a Cairo military sports complex, according to a statement posted on the military's official Facebook page.
Earlier in the day, 11 people were wounded as masked gunmen targeted anti-government activists.
Last week, six people died and hundreds were wounded in clashes between supporters of Mr. Morsi and the opposition in the worst violence in the country since its revolution in 2011.
"The country is extremely divided, and it's under these circumstances that we are being asked to vote," said Khaled Fahmy, history department chairman at The American University in Cairo.
"It's not the usual division of any country that precedes a highly contested vote," Mr. Fahmy said, adding that he is "very anxious" about the referendum. "It's very different in the sense that what we are voting on is the rules of the game, and we are not even agreeing on that."
A contentious vote
On Tuesday, Mr. Morsi restricted which polling stations would be open to ensure "fairness in the voting process," a government statement said.
Meanwhile, a main association of judges announced that 90 percent of its members would not oversee the referendum, as is customary in Egypt.
Even if the referendum goes forward, it is unclear whether it will be legally binding without them, analysts said.
"Some judges will probably agree to supervise, and many others will boycott this," said Mazen Hassan, political science lecturer at Cairo University. "If this happens, many Egyptians, especially the non-Muslims, will raise questions about the integrity of the vote.
"Morsi antagonized the entire judiciary with his decisions these past couple of weeks, and many of the judges are just deciding to fight back. They think the whole process is unconstitutional, illegal and illegitimate, and that's their way of saying no."
The judiciary has said it will decide Wednesday whether to participate in the referendum.
The opposition is hoping that if it decides not to participate, Mr. Morsi will halt the vote, which is one of its key demands.
"I'm here to push for building this country on the proper foundational constitution it deserves, written by a diverse body," said Sherief Hassan, 26, a telecommunications engineer who protested Tuesday at the presidential palace. "There are fewer freedoms than in the 1971 constitution. The bigger problem is in who wrote it and the illegal process they wrote it by, not what's in it so much."
"[The constitution] will most likely pass with 'yes,' but I am here because I have some hope," the protester added.
In Nasr City, tens of thousands of Islamists rallied in favor of the charter, accusing the opposition of being supporters of former President Hosni Mubarak, who was ousted by a popular revolt in February 2011.
"In the last election, I said 'no' to Morsi, but I am with him because he is the legal president," said Abdallah Omar, a chemist in Cairo. "If there is someone who wants to say 'no' to the constitution, that is no problem. But the problem is with people who want to stop progress."
Political, economic uncertainty
Supporters of the constitution say the country must hold this referendum and pass a new charter in order to move forward in its political transition.
Opponents of the proposed constitution say it lays the foundations for an Islamist state that would restrict freedom of speech and rights for women and minorities while granting clerics a say in interpreting law.
Many secular members, as well as minority Coptic Christians, walked out of the committee that drew up the constitution late last month.
A question mark hangs over whether opposition groups will campaign for a "no" vote or for a boycott of the referendum.
Analysts said low voter turnout could seriously damage the credibility of the constitution if it passes.
"The government may say, 'Take it or leave it. We invited you. If it's your fault, we will proceed without you,'" said Mr. Fahmy. "But the results then will cast serious doubt on the whole legitimacy of the vote if the opposition is not around, if the Copts are not around."
Still, the government is betting on voter support of the constitution in order to bring stability to a country where many are growing weary after close to two years of political instability, economic uncertainty and public unrest.
Others said it was necessary to fight for Egypt's future.
"This is the first time I join a protest. My children protested in Tahrir, but I never did but Morsi provoked me. I had to protest," said Ayda Hasaneen, 50, marching toward the presidential palace. "I hope there will be a fair constitution, not for me, but for my children.
"My son fought Mubarak's regime, my other son fought Morsi's rule outside the palace on that bloody Wednesday. I'm here today for them."
• Ruby Russell reported from London. Marwa Nasser and Sarah Lynch, both in Cairo, and Josie Le Blond in Berlin contributed to this article, which is based in part on wire service reports.