An attempt by Mr. Morsi on Monday to soften his edict, by reaffirming his deference to Egyptian courts, did little to constrain the crowd, which some estimates put at hundreds of thousands of people. In scenes that were reminiscent of the popular uprising against President Hosni Mubarak, and that signaled the country’s current widening divides, the protesters dusted off old taunts for Mr. Morsi, the country’s first freely elected leader.
“Leave,” they chanted. “The people want the fall of the regime.”
The president’s opponents turned out large numbers in several other cities, and clashed at times with his supporters, including in Mahalla el-Kubra in the Nile Delta, where more than a hundred people were reportedly injured. The Brotherhood also reported attacks on several of its political offices.
Most significant, though, was the turnout in Tahrir Square, where Egypt’s secular-minded opposition appeared to have momentarily overcome its divisions, bolstering its numbers with new allies among people implacably opposed to the Brotherhood, in an effort to muster a serious, visible challenge to Egypt’s Islamist groups.
It remained unclear whether Tuesday’s numbers signaled a new movement, or a moment. Islamists have repeatedly won at the polls since the fall of Mr. Mubarak, and the Brotherhood has shown its ability to turn out large crowds with little difficulty.
On Tuesday, the Brotherhood mocked the gathering in Tahrir Square, dismissing the protesters as “remnants” of the Mubarak government on a television channel associated with the group and playing down their numbers on Twitter.
The taunts were ignored in Tahrir Square, where the crowd chanted, “The square is full without the Brotherhood.”
The gathering was prompted by an edict released by Mr. Morsi last week that his decisions would be above judicial review, a move that essentially removed the last check on his power, since Egypt’s Parliament had earlier been dissolved by the courts.
Though Mr. Morsi framed the decree as an attempt to insulate Egypt’s constitutional assembly from being dissolved by Mubarak-era judges, it was quickly attacked as a power grab and a worrying return to autocracy. On Monday, through his spokesman, Mr. Morsi again tried to explain his intentions, saying he would work within judicial precedents to hold back efforts to dissolve the constituent assembly, rather than putting his power above judicial scrutiny.
Even as Mr. Morsi tried to placate the country’s judges, Egyptian television on Monday showed the growing polarization of the country in split-screen coverage of two funerals, each for a teenage boy killed in clashes set off by Mr. Morsi’s edict.
“Now blood has been spilled by political factions, so this is not going to go away,” said Rabab el-Mahdi, an activist and professor at the American University in Cairo, adding that these were the first deaths that rival factions had blamed on one another and not on the Mubarak government’s security forces since uprising began last year.
Despite Mr. Morsi’s attempts at clarification, opposition leaders went ahead with Tuesday’s protest. Some said that respect for the judiciary was now only a small part of their cause, and that their goal was to abort the current Islamist-dominated constituent assembly.
Many protesters treated the occasion as a referendum on Mr. Morsi’s rule, saying he and his prime minister had failed to make important changes, like reforming the Interior Ministry.
“I voted for Mr. Morsi,” said Emad Abdel Kawy, 35, a computer engineer. “It seems like he doesn’t know what he’s doing. You expect a revolution to bring revolutionary actions. It didn’t happen.” And like many here, Mr. Abdel Kawy blamed the Brotherhood, which Mr. Morsi helped lead before becoming president.
“It’s clear he doesn’t make the decisions,” he said of Mr. Morsi. “The decisions come to him.”
The gathering brought together the revolution’s hardened activists with their former foes, including supporters of the Mubarak government. Some said that the strange new alliances were just a necessary result of Egypt’s confusing, emerging politics. Yosra Mostafa, a 28-year-old activist, said she realized that some of Mr. Mubarak’s supporters had turned out simply because they sought a return to power.
“I don’t mind being on their side to oust a dictator,” she said, speaking of Mr. Morsi.
The show of unity masked deep divisions between the opposition and other groups and even in them, Ms. Mahdi said.
“This is not a united front, and I am inside it,” she said. “Every single political group in the country is now divided over this. Is the decree revolutionary justice or building a new dictatorship? Should we align ourselves with felool” — the term for the remnants of the old government — “or should we be revolutionary purists?”
Yasser el-Shimy, an Egypt analyst at the International Crisis Group, argued that the persistence of protests against Mr. Morsi reflected in part the failure of the opposition to accept its own recent election defeats, including of the parliamentary and presidential elections.
“It has never come to terms with these defeats, so it tries to delegitimize the Muslim Brotherhood,” he said.
Mayy El Sheikh and Mai Ayyad contributed reporting.