Hundreds have been injured during clashes between rival protesters in Cairo's Tahrir Square on Friday, with pro and anti-Muslim Brotherhood demonstrators locking horns.

Tensions were alleviated after the Brotherhood supporters started to leave by the afternoon. An Ahram Online reporter, however, said that two the Islamic group's empty buses were set alight.

Secular groups, who remain in the Square up till press time following the departure of the Brotherhood supporters, took to the square for 'Accountability Friday' primarily to demand a more representative Constituent Assembly.

On the other hand, the Brotherhood supporters, who came from different governerates, were there to condemn Wednesday's acquittal of former regime figures accused of orchestrating the Battle of the Camel during the Egyptian Revolution.

Omar Rashid, the ambulance field supervisor in Tahrir Square, confirmed to Ahram Online reporter that around a hundred had been hospitalised by late afternoon, mostly with head injuries. "Hundreds more suffered different injuries," he added.

A number of people were shot with pellets by unknown assailants on Talaat Harb Street, an Ahram Online correspondent at the scene reported, while Molotov cocktails and rocks were being thrown in both Mohamed Mahmoud Street and Talaat Harb Street near Tahrir Square.

Clashes began in the early afternoon when some protesters began chanting against the Muslim Brotherhood and President Mohamed Morsi. They were attacked with stones in response and a stage belonging to Hamdeen Sabbahi's Popular Current was destroyed.

"Those who destroyed the stage are chanting for Morsi and beating up whoever chants against him," Mohamed Waked, a leading member of the National Front for Justice and Democracy, said via Twitter.

In an interview with ONTV Live satellite channel, Amin Iskander of the Popular Egyptian Current held the Muslim Brotherhood responsible for the clashes because it had called for a protest in Tahrir Square even though anti-Brotherhood groups had already planned a protest at the same venue.

"Our protest was planned a long time ago. Our demands were clear before the verdict of the Battle of the Camel took place. [The Brotherhood] made a mistake when it decided to hold a protest in Tahrir Square today," Iskander said.

Iskander also blamed the interior ministry for failing to protect peaceful protesters. Their decision to stay away from the square for the sake of "neutrality" had only benefited the Brotherhood, he said.

Security forces were absent from the square and the surrounding streets all day, an Ahram Online reporter confirmed.

"If Mubarak was a dictator, what is happening now means Morsi a "sacred' dictator," Iskander added.

The April 6 Youth Movement also condemned the Brotherhood and urged the group to control its members.

"The Muslim Brotherhood were firing pellets," leftist activist Kamal Khalil said. "They are trained militias; they are the one who initiated the fighting today."

Opposition journalist Hamdy Qandil called on the Muslim Brotherhood to remove its members from the square and claimed via Twitter that the actions of the Brotherhood on Friday would not have been attempted by the pre-revolution National Democratic Party.

The Muslim Brotherhood has strenuously denied responsibility for the clashes, claiming its members were not in the square before 4pm.

"Our members haven’t attacked anyone, the people fighting are supporters of the president," Brotherhood spokesperson Mahmoud Ghozlan said.

Essam El-Erian of the Brotherhood's Freedom and Justice Party said its members were told to gather at the High Court in downtown Cairo at 4pm.

"We are not involved in Tahrir clashes, and none of our members were there [during the afternoon]," the Brotherhood claimed on its official Twitter page.

Protests also took place in Suez to criticise the performance of President Morsi and in Alexandria to demand a more representative Constituent Assembly

Protests calling for similar demands took place in the Nile Delta cities of Mansoura and Al-Mahalla Al-Kobra, where anti-Brotherhood slogans were chanted.

The groups which initially announced they would be participating in the 'Accountability Friday' protest were: National Association for Change, Popular Egyptian Current, Constitution Party, Egyptian Social Democratic Party, April 6 Youth Movement, Democratic Movement, Democratic Revolutionary Alliance, Egyptian Socialist Party, Egyptian Communist Party, Socialist Popular Alliance Party, Tagammu Party, Workers and Peasants Party, Socialist Youth Union, Popular Democratic Movement, Mina Daniel Movement, Popular Revolutionary Movement, Justice and Freedom Movement and Peaceful Front for Change.

The Egyptian Democratic Workers Conference, an umbrella of number of independent trade unions established after the ouster of Mubarak in February 2011, also issued a statement of other demands related more specifically to workers rights, calling for a march to Tahrir Square at noon.