In his first televised speech as leader, Foued Mebazaa highlights the need for the ruling RCD party to separate from the state Reuters

Tunisia's interim president, Foued Mebazaa, yesterday vowed "a complete break with the past" to calm fears that the revolution was being hijacked by the presence of the dictatorship's ruling party in the interim government.

In his first televised speech, Mebazaa promised a "revolution of dignity and freedom" following the ousting of Tunisia's dictator president, Zine al-Abidine Ben Ali, after four weeks of street protests. Mebazaa promised to honour "all the legitimate aspirations of the uprising".

Yesterday, as the interim cabinet held its first meeting, around 500 protestors, mostly the radical left and trade unions, took to the streets in central Tunis demanding that the ruling RCD party be excluded. But the mood in the capital was lightening.

Unlike previous days, the protesters on Bourguiba Avenue were not teargassed or beaten but were instead allowed to stand peacefully protesting until nightfall. Political prisoners, including a key dissident journalist, began to be released, the curfew was shortened, cafes reopened and people milled to work. In the narrow streets of the old medina, tourists were bartering over bags.

On Bourguiba Avenue, Azizi Tej stood in the crowd of demonstrators chanting "Tunisia is free". An activist in the once banned Islamist Ennahda party, he had been imprisoned three times, tortured, had staged a series of hunger strikes, and had now taken to the streets with the secular radical left. He wanted the remnants of Tunisia's old regime, the RCD party, to be excluded from the temporary caretaker government.

"The Islamists want democracy," Tej said. "Lots of us were tortured, it was our Guantánamo Bay. We've paid a high price and now some people want to paint us as monsters, we're not. My religion teaches that I must accept others. We're proud to share the same God, Jews and Christians are our brothers. We don't refuse women's freedoms, we don't refuse tourism – people would die of hunger if we didn't have tourism."

"The government has to listen to the street," said Salem Ben Yahia, a film-maker and former political prisoner. "We don't want our revolution hijacked. We forced a dictator out the door and now he's come back in the window. His old ministers are still in a majority in this transition government and that has to change. Police have already shot at us and beaten us to stop us protesting, but we come back again like a tide." In his pocket he had a hankie doused in vinegar to protect himself from teargas. But riot police were standing back.

Ministers were last night trying to hold together the government after three trade union ministers quit and political sources said minor changes would have to be made to the government in the coming days. A fourth minister, Mustafa Ben Jaafar, head of the small Democratic Forum for Freedom and Labour, who had hesitated over a full resignation, did so yesterday. "We have pulled out of the government officially," his party said.

One insider at the transport ministry said nothing had changed in the civil service, the state apparatus was still in place and functionaries remained party members. "You had to be in the party to progress in your career. At work, we still daren't even talk about the revolution, people are still afraid of talking," he said.

Tunisian state television reported the government had released 1,800 prisoners sentenced to less than six months for minor offences. Chebbi of the PDP opposition party said these included political prisoners, particularly members of the banned Islamist movement Ennahda. But figures were not available of how many people had been released. Secrecy under the ousted dictator Ben Ali meant that the number of those detained for political reasons was never made public.

A further insight into the events of last week was provided by a government minister, who told Reuters yesterday that Ben Ali had informed prime minister Muhammad Ghannouchi that he was considering returning from exile, but Ghannouchi had told him that was impossible. Najib Chebbi, an opposition leader who is now regional development minister, said the exchange took place by telephone.

Meanwhile, investigations were beginning into the scale of violence during the weeks of brutally repressed demonstrations which led to the revolution. The UN estimated that at least 117 people died, including 70 killed by live fire, in five weeks of bloodshed linked to demonstrations which led to the ousting of Ben Ali.

UN human rights officials will go to Tunisia next week to help investigate the violence and advise the new coalition government on justice and reforms, UN high commissioner for human rights Navi Pillay said yesterday.

Pillay said her human rights team, authorised by the government, would begin work immediately: "We've never been able to act so quickly before."

As Switzerland moved to freeze Ben Ali's assets, demonstrators in the Tunis crowd included people whose homes had been appropriated by the family of Ben Ali and his wife. A businessman said his 13th century villa in a prime Tunis suburb was taken over by a relative of the first lady, Leila Trabelsi. He had complained to the justice system and was harassed and had his passport taken away. "We want the government to return the people's wealth that they plundered," he said.

France said it had intercepted a shipment of riot gear, including tear gas canisters and bullet-proof vests, ordered by Ben Ali just before his downfall.

Moncef Marzouki, the leader of a small opposition party who returned to Tunisia from exile in France this week, visited the grave of the unemployed graduate and vegetable seller, Mohamed Bouazizi, who set fire to himself in an act of protest and started the wave of unrest which toppled Ben Ali.

Marzouki, who plans to run for president, also went to where Bouazizi set himself on fire in the town of Sidi Bouzid. About 300 people greeted him, with banners urging the interim prime minister to quit and "The people demand that Ben Ali's people leave!"

At the small Tunis demonstration, people vowed to keep up pressure for the interim government to feature more than a handful of opposition figures. "People died, are we going to waste their blood?" asked Solef, an unemployed graduate who sells sweets. "It's our duty. People here walk with their heads held high."