Police back on the streets of Cairo amid protests. Reuters

The fiercest street fighting seen in central Cairo since the fall of Hosni Mubarak has left more than 1,000 people injured, as popular dissatisfaction with the military-led transitional government boiled over into violence.

In what analysts have labelled a "critical turning point" in Egypt's ongoing revolution, several thousand people clashed with heavily armed riot police in and around Tahrir Square on Tuesday night, leading to dozens of arrests.

The Supreme Council of the Armed Forces blamed "sedition" for the unrest and vowed to hunt down those responsible. Throughout Tuesday night and yesterday morning protesters chanted demands for the resignation of Egypt's de facto leader, Field Marshall Mohammed Hussein Tantawi, as security forces fired tear gas and rubber bullets into the crowds.

The demonstrations follow five months of accumulated frustration among many sections of the Egyptian public over the slow pace of reform since an 18-day uprising toppled Mubarak and ushered in a military junta, which has promised to hand over power to a democratically elected civilian government later this year.

There has been particular anger over the perceived lack of accountability for stalwarts of the old regime. Although some former government ministers have been found guilty of corruption, the trials of the former justice minister Habib al-Adly and Mubarak himself – the two men many hold responsible for the killing of unarmed demonstrators by police – are yet to take place, while police officers accused of unlawful killing continue in their posts and families of the victims report being bribed or threatened to drop their legal cases.

"These clashes are the result of Egypt's new regime trying to reproduce the authoritarian policies and brutal, unaccountable security apparatus that were the tools of dictatorship for the old regime, and they are a critical turning point for the revolution," said Nabil Abdel Fattah, a political analyst at the al-Ahram Centre.

"We are seeing the same tactics – tear gas, bullets, state violence – that Mubarak used, and more importantly we are hearing the same discourse from Egypt's interim rulers. 'This is a plot to destabilise the country, there are shadowy groups trying to sow discord,' claim the cabinet and the army generals, but where is this plot and who is writing it? In fact the only 'plot' is the anger of the people against a political elite that has initiated no real change, and a government that marginalises the poorest in Egyptian society and has little credibility in the eyes of the masses."

The Guardian has spoken to residents in the downtown area who claim that central security forces (CSF) asked them to come and help defend the interior ministry from "criminal thugs" who were allegedly smashing up shops and cars in the area. "We stood with the police for some time and threw rocks at the civilians on the other side," said one man who preferred not to be named.

"We genuinely thought the CSF needed our help – they told us that if the thugs saw ordinary people standing side by side with the police, they would be scared off and calm would be restored. But the CSF then made the situation much worse by deliberately firing into the crowds, which brought lots of peaceful protesters on to the scene and it turned into a big battle. I don't know why the CSF did that but it felt like they wanted to make trouble."

Demonstrators claim that far from being criminals, the civilians on the street were families of those killed during January's uprising. For the past few months the terms "thugs", "criminals" and "counter-revolutionaries" have been regularly deployed by the authorities to describe anyone deemed to be provoking instability in the post-Mubarak era.

The events of the past 48 hours are likely to increase the pressure on the interim prime minister, Essam Sharaf.

"Sharaf is honest and gentle but has offered nothing substantive in terms of change; he's been reduced to a mouthpiece of the military and he must resign," said Abdel Fattah.

"People are realising that despite the rhetoric, no reform is going to be initiated by the political elite. It has to come from the street and I think the next major demonstration in Tahrir which is planned for 8 July will be an example of that."