Gunmen opened fire on Cairo's Tahrir Square early this morning, setting the stage for more violence in the Egyptian capital as supporters and opponents of President Mohamed Morsi prepared to hold rival rallies.
At least nine opposition protesters were injured after masked attackers fired birdshot and threw petrol bombs at their camp, Reuters reported. Egypt's Ahram Online said as many as 16 were wounded, one in the head.
Police cars were soon deployed to guard the square for the first time since protests broke out last month.
Further clashes were feared during planned demonstrations later in the day, the BBC said. The ruling Muslim Brotherhood and a number of opposition groups each held marches through Cairo over the controversial referendum on a new constitution, which Morsi has set for Dec. 15.
Six separate opposition marches were set to converge on the presidential palace to demand that Morsi call off the vote and start work on a new draft of the constitution, this time with greater input from liberals, secularists, womens' rights activists, Christians and other groups that say they're underrepresented.
Meanwhile, the Brotherhood had called for two "million-man" marches to show support for the referendum and urge voters to approve the draft text as it is.
From Cairo, GlobalPost's Erin Cunningham said the protests have remained relatively calm. "No major developments around the protests tonight so far. They're happening, and they're big. But no clashes," she wrote on Tuesday night.
She added: "Protestors did tear down at least part of the concrete wall the presidential Republican Guard built several days ago in defense of the palace. They broke through the security cordon this evening (as they've done several times), but they did not storm the palace."
The danger was that rival protesters would cross paths. Last time that happened, last Wednesday outside Morsi's palace, seven people ended up dead and hundreds more injured.
Outside Cairo, protests were also planned Tuesday in the cities of Alexandria and Assiut, the BBC said.
Cunningham said concern for many in Cairo was already focused on events planned for Wednesday, the day Morsi has proposed rival factions meet with army generals for "national dialogue."
"Spokesmen for president Mohamed Morsi, and for the Muslim Brotherhood, initially seemed to be caught off-guard by the announcement. Now they're waffling back and forth issuing contradictory statements on whether or not Morsi will be attending the dialogue session," she wrote.
"That's a pretty serious indicator that things are going badly, and that, possibly, the army believes there will be serious instability if the situation continues as it is. That the defense minister called this meeting independent of the presidency is also an ominous sign."
More from GlobalPost: Morsi gives Egypt's army power to arrest civilians
GlobalPost's Erin Cunningham contributed reporting from Cairo.