Tens of thousands of protesters have filled Cairo's Tahrir Square to denounce a move by Egypt's ruling generals to seize sweeping powers.Last weekend, the military issued decrees dissolving parliament and claiming all legislative power.Critics and analysts said their actions amounted to a military coup.In a TV statement, the military warned that "any attempt to manipulate" the results of the recent presidential election would not be tolerated.The Supreme Council for the Armed Forces (Scaf) said its decision to issue the decrees was "a must" and the nation was overwhelmed by a state of confusion.Results delayedIslamist, secular and youth groups backed a call by the Muslim Brotherhood for protests across Egypt after Friday prayers.The cleric leading prayers in Tahrir Square said Mohammed Mursi, the Brotherhood's presidential candidate, was the clear winner in presidential elections last weekend, the Associated Press reports.Earlier, Mr Mursi's opponent, former Prime Minister Ahmed Shafiq, said he was confident of victory.Results from the run-off election were originally due out during the week but have been delayed.Thousands of people, mostly Islamists, have demonstrated for three consecutive days against the two decrees issued by the Scaf.The first decree ordered parliament to be dissolved. It came after a Supreme Constitutional Court ruling that the law on elections to the lower house was invalid because party members had been allowed to contest seats reserved for independents.The second decree gave the generals complete control over legislation and military affairs until fresh parliamentary elections are held.The justice ministry has also granted soldiers the right to arrest civilians for trial in military courts until the ratification of a new constitution.Human Rights Watch has said the moves suggest there will not be a "meaningful" handover of power to a civilian administration by 30 June and conditions "ripe" for further human rights abuses had been created. 'Media manipulation'Meanwhile, the BBC's Jon Leyne in Cairo reports that opponents of the Brotherhood are now running a concerted campaign to discredit its claim that Mr Mursi won last weekend's presidential election run-off.On Tuesday, the Brotherhood's Freedom and Justice Party (FJP) announced that Mr Mursi, its chairman, had received 51.74% of the vote, citing official figures provided to both candidates by the Higher Presidential Election Commission (HPEC).But on Thursday evening, Mr Shafiq made his first public appearance since the election to claim victory for himself."I am fully confident that I will be the legitimate winner," he told supporters at a Cairo hotel.Mr Shafiq is a former air force commander who served briefly as former President Hosni Mubarak's last prime minister.Media sympathetic to Mr Shafiq and the Scaf have begun to demonise the Brotherhood, our correspondent says.One journalist, Gamal el-Ghetani, said the attempt by the Brotherhood to gain power was like the rise of Adolf Hitler in Germany in the 1930s. The newspaper al-Dustour said the Brotherhood planned a bloodbath if Mr Mursi was not declared the winner.Members of the HPEC have now suggested a result may now be declared on Sunday. An announcement had been expected on Thursday, but officials said hundreds of complaints had been received from the two candidates."I have faith in the judges of Egypt, but too much delay will raise question marks," Saad al-Katatni, a Brotherhood leader and speaker of the dissolved lower house of parliament told al-Jazeera. "The result is already known and it is Mohammed Mursi."