The tents are going up again in Tahrir Square.

Iconic symbols of the revolutionary fervour that filled Cairo two years ago, sweeping away a dictator and ushering in the election of an Islamist president, dozens of tents have popped in the central square as an ominous sign of the deep divisions that remain and the potentially violent protests that could break out over the coming days.

Anger – over rising prices, gas shortages, a moribund economy and the growing political dominance of the Muslim Brotherhood – has reached a tipping point. Opposition groups have called for massive demonstrations on Sunday, the first anniversary of the inauguration of Mohammed Morsi as the country's first democratically elected president. Mr. Morsi's supporters from the Brotherhood plan their own advance demonstration on Friday. The army has warned it might step in if the street protests spiral out of control, raising the risk of more disarray and violence.

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The main opposition coalition rejected the President's offer for dialogue on Thursday, and insisted on early elections. The National Salvation Front, in a statement read by Nobel Peace Laureate Mohamed ElBaradei, said Mr. Morsi's speech to the nation on Wednesday showed "a clear inability to acknowledge the difficult conditions in Egypt because of his failure in running the country since he took office a year ago."

He vowed that "the Egyptian masses will go out in their millions in peaceful protests that fill the streets and squares of Egypt on Sunday."

Bitter feelings and mutual hostility have hardened in the past year, which has seen hundreds of street protests and deadly clashes between the Mr. Morsi's Muslim Brotherhood and its opponents. The President's critics are accusing him of freezing out secular and liberal voices in pursuit of an agenda to restrict individual freedoms. His supporters call those critics Hosni Mubarak loyalists and Communists trying to destabilize the country.

"As corrupt as Mubarak was, he was better than Morsi," said Mohammed Mustafa, who collects signatures for the Tamarod, or "rebel," campaign. "Now there is no security, no transparency and inflated prices." Tamarod organizers say they have collected more than 15 million signatures in its petition drive – although that would be more than the 13. 2 million people who voted for Mr. Morsi – in its campaign to force new elections.

Mohammed Nassar, a Muslim Brotherhood supporter, blamed the opposition for splitting Egyptian society. "There is a war between Islamists and Communists, who call themselves liberals," he said as he sat in a coffee shop near Tahrir Square. "The opposition says: 'If you're not with us, you will be targeted.'"

Many people fear the worst for the weekend. Banks buzz with people withdrawing huge sums of money, families crowd stores stocking up with enough non-perishable food to last for weeks and some businesses are preparing for potential damage and looting. The luxury Semiramis Intercontinental Hotel, damaged in clashes between police and protesters in January, has installed a protective gate. Fights are breaking out in gas stations where drivers wait for hours in a sometimes vain attempt to fill their gas tanks before the demonstrations.

The potential intervention of the army, which ran Egypt between the ouster of Mr. Mubarak and Mr. Morsi's inauguration, has added another worry.

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"It's the same army that raped women and called us thugs," said Ali al Ziat, an opposition activist. The graffiti here bears witness to the people killed by the military," he added, pointing to a wall that is splashed with brightly painted revolutionary scenes and faces of those who died in the uprising.

In his speech on Wednesday night, Mr. Morsi told his opponents to use elections rather than protests to try to change the government and counselled the military to focus on improving its capabilities and defending the nation. As his voice boomed from radios and loudspeakers, thousands of people gathered to hear him shouted, "Irhal," or "leave," and some held their shoes up in a sign of disdain as red fireworks exploded.

Mr. Morsi's first year in office has been marked by political deadlock and perpetual conflict with the judiciary. The high court dissolved the Islamist-dominated parliament last year and earlier this month invalidated a panel appointed by the President that had drafted a new constitution. Egyptian liberals, suspicious that Mr. Morsi could not shake the ideology of the Brotherhood, say he has tolerated attacks on opponents and a rising sectarianism.

Mr. al Ziat said he fears religiously motivated violence will continue under Mr. Morsi, alluding to the recent Sunni mob killing of four Shiites that closely followed a conference where the religious minority was called "filth" by a Sunni cleric. Mr. Morsi, who was sitting on the same stage, did not speak up.

"Religion and politics can't mix – not like this," Mr. al Ziat said. "The state is being Brotherhood-ized. I'm proud of Islam, my religion, but Morsi's Islam is not mine."

With a report from Associated Press