CAIRO — Thousands of supporters and opponents of Egypt’s new Islamist president clashed in Cairo’s Tahrir Square Friday in the first such violence since Mohammed Morsi took office more than three months ago, as liberal and secular activists erupted with anger over accusations the Muslim Brotherhood was trying to take over the country.
The two sides hurled stones and chunks of concrete and beat each other with sticks for several hours, leaving more than 100 injured, according to the state news agency.
Two buses used by the Brotherhood to bring in supporters were set aflame behind the Egyptian Museum, the repository of the country’s pharaonic antiquities, and thick black smoke billowed into the sky in scenes reminiscent of last year’s clashes between protesters against the regime of then-leader Hosni Mubarak and his backers.
The melee erupted amid two competing rallies in Tahrir. One was by liberal and secular activists to criticize Morsi’s failure to fulfill promises he had made for his first 100 days in power, the other had been called by Morsi’s Muslim Brotherhood.
The clashes occurred as criticism among leftists, liberals, and secularists against Morsi has been growing since he was inaugurated more than three months ago as Egypt’s first freely elected president. Opponents accuse Morsi, the Brotherhood, and other Islamists of trying to impose their dominance and Islamize the state, including through the writing of a new constitution.
Some Egyptians are also frustrated that Morsi, a longtime Brotherhood figure, has not done more to resolve the multiple problems facing the country — from a faltering economy and fuel shortages to tenuous security and uncollected piles of garbage in the streets.
Morsi boasted earlier this week in a nationally televised speech that he had carried out much of what he had promised for his first 100 days, and his supporters say he needs time in the face of overwhelming difficulties inherited from Mubarak’s authoritarian and corruption-riddled rule.
One anti-Brotherhood protester in Tahrir, Abdullah Waleed, said he had voted for Morsi in this year’s election to prevent his opponent — a longtime Mubarak loyalist — from winning.
‘‘Now I regret it because they are just two faces of the same coin,’’ Waleed said. ‘‘Morsi has done nothing for the revolution. I want to say I am so sorry for bringing in another repressive regime.’’
Violence also broke out in the industrial city of Mahalla el-Kobra, a hotbed of regime opponents and labor activists in the Nile Delta renowned for its history of revolts against Mubarak.
Protesters torched headquarters of the Muslim Brotherhood in the city and set fire to Morsi posters.
Days ago, liberal and leftist groups had called for Friday’s protest in Tahrir to demand accountability over Morsi’s three-month rule. They also demanded greater diversity on the panel tasked with writing Egypt’s new constitution, which is packed with Brotherhood members and other Islamists who have proposed provisions opponents say greatly suppress civil liberties.
The Brotherhood called for a separate rally to denounce the acquittals earlier this week of 24 former senior figures from Mubarak’s regime who had been accused of organizing a deadly attack on protesters during last year’s Jan. 25-Feb.11 wave of protests that led to Mubarak’s ouster.
The Brotherhood rally was to call for judicial reforms and to support a move by Morsi on Thursday to remove the prosecutor-general, who has been widely criticized for preparing shoddy cases against Mubarak-era politicians and police. Buses organized by the Brotherhood had brought in supporters from the provinces for the rally.
But the secular camp accused the Brotherhood of holding the gathering to ‘‘hijack’’ the square from their anti-Morsi protest.
The violence erupted when Morsi supporters stormed a stage set up by the rival camp, angered by chants they perceived as insults to the president. The Islamist backers smashed loudspeakers and tore the wooden stage down, witnesses said.
The uproar ensued as more supporters of the liberal-secular rally poured into the square. Young men from both sides tore up chunks of concrete and paving stones to hurl while others hit each other with sticks.
Gunshots were heard. Youths making V-for-victory signs with their hands set fire to two empty buses of the Brotherhood.
‘‘My conclusion here is that Morsi is just the president of the Brotherhood, that’s all. We are back to square one,’’ since Mubarak’s fall, said Sayed al-Hawari, who carried a plank of wood as a shield against the volleys of stones.
A liberal protester, Rania Mohsen, said, ‘‘We are here against turning the state to a Brotherhood state. . . . We do not want to replace the old regime with a new like the old one.’’
A Morsi supporter, in turn, accused the other camp of being ‘‘thugs’’ who chanted against the leader of the Brotherhood and harassed the Islamists during noon prayers in Tahrir.
‘‘We have to give Morsi a chance,’’ 19-year-old Moez Naggar said. ‘‘The more protests we have, the less we can expect from him.’’