ISTANBUL (Dispatches) -- Thousands of protesters on Sunday celebrated after police withdrew from Istanbul's Taksim Square, the focal point of nationwide protests against Turkey's government.

The government, while acknowledging some excesses by police in two days of clashes, called on the demonstrators to leave the streets after protests in 48 cities.

Rights groups denounced police violence, with Amnesty International saying that there had been two deaths. Turkey's Western allies Britain and the United States have called for the government to exercise restraint.

According to official figures, the clashes over the last few days have left dozens injured. Amnesty put the figure in the hundreds and said that some protesters had been left blinded by the massive quantities of tear gas used by police.

Overnight Saturday, however, protesters in Taksim Square were celebrating their victory over the police, dancing and singing, with some even launching fireworks.

"Government, resign!" protesters shouted as the police retreated.

"We are here Tayyip, where are you?" they chanted, taunting Prime Minister Recep Tayyip Erdogan.

What began as an outcry against a local development project snowballed into a broader protest against what critics say is the government's increasingly conservative and authoritarian agenda.

And since the first clashes on Friday, the unrest has spread to dozens of other cities across the country.

On Saturday, police in Ankara blocked a group of demonstrators from marching on parliament and the prime minister's office.

Speaking at a rally Saturday, Erdogan acknowledged: "It is true that there have been some mistakes, extremism in police response."

But he added: "I call on the protesters to stop their demonstrations immediately."

He also vowed to push forward with controversial plans to redevelop the square -- the issue that sparked the protests.

The interior ministry promised legal action against police officers who had acted "disproportionately".

At Taksim Square, a popular tourist destination and traditional rallying site in Istanbul, the mood was defiant.

"We are still ruled by a prime minister who thinks people are lambs and declares himself the sultan," said 19-year-old law student Batuhan Kantas, sitting exhausted on the ground.

Turkey's President Abdullah Gul called for restraint on both sides.

Interior Minister Muammer Guler said that 53 citizens and 26 police officers had been injured across the country, with one person in intensive care at an Istanbul hospital.

The minister also said police had detained 939 protesters in more than 90 demonstrations in 48 cities, though some had later been released.

Officials said a dozen people were being treated in hospitals.

But Amnesty International spoke of reports of two deaths and more than a thousand injured, although there was no official confirmation of those figures.

In a statement, it said they opened its Istanbul offices, near Taksim Square, to give sanctuary to protesters and 20 doctors were treating injured protesters there.

Amnesty's Europe director John Dalhuisen said police excesses in Turkey had become routine.

"But the excessively heavy-handed response to the entirely peaceful protests in Taksim has been truly disgraceful," he added.

Human Rights Watch also suggested the real casualty figure was much higher than the official figures. One protester had lost an eye after police shot him with a plastic bullet, the group reported.

The U.S. State Department called on Turkey to uphold "fundamental freedoms of expression, assembly and association, which is what it seems these individuals were doing".

"We urge authorities in Turkey to exercise restraint and not to use tear gas indiscriminately," the British foreign office tweeted on Saturday.

The Istanbul protest began as a peaceful sit-in at Gezi park across the iconic square.

The demonstrators had been preventing workers from razing some of the park's 600 trees, the last patch of green in the commercial area, to make way for the restoration of Ottoman era military barracks. Residents fear that the barracks will be turned into a shopping mall.

But the demonstration soon took a violent turn after police fired rounds of tear gas to disperse the protesters.

In a scene reminiscent of the Arab Spring, thousands of people flooded Istanbul's main square after the crackdown on the anti-government protest turned city streets into a battlefield clouded by tear gas.

He has called the protesters a "minority" that was trying to forcefully impose demands.

Private NTV television reported that protesters built barricades at entrances to the square to prevent police from returning.

In Ankara, thousands congregated at a busy shopping street, jovially singing, waving Turkish flags, and frequently breaking into calls for Erdogan to resign. One group jokingly called on police to fire more tear gas at protesters suggesting they had grown addicted and "were going crazy" without it.

"We have had it up to here with him," said protestor Neslihan Yildirim, raising her hand to her chin. "Constant oppression... All the intervention in our lives."

Scenes at the square brought to mind Cairo's Tahrir Square, the center of an uprising that ended Egyptian President Hosni Mubarek's rule.

The protests were more of a warning, according to Ahmet Cigdem, a professor of sociology and political science at Ankara's Gazi University.

"The people showed that the government's rule is not guaranteed just because they obtained some 50% of the votes and just because there is no powerful political opposition in Turkey," Cigdem said.

"These protests have clearly showed what the people reject. They are saying 'Don't force your political, sociological and cultural impositions on our lives. Don't try to shape my thoughts and my beliefs," he said.

The government's policy on Syria remains unpopular, with many believing its open support to rebels fighting Syrian President Bashar Assad's government has put Turkey's security at risk. On May 11, twin car bombs at a border town the government blamed on Syria killed 52 and sparked anti-government protests.

The protest was also seen as a demonstration of the anger building toward Turkish police, who have been accused of using inordinate force to quash demonstrations and of using tear gas excessively.

In Syria, Information Minister Omran al-Zoubi said Erdogan's suppression of the peaceful protests in Turkey was "illogical and reveals his detachment from reality".

Echoing words that Erdogan has used against Syrian leader Assad, al-Zoubi said it is unjustified that Erdogan should defy his people.

Iran’s Foreign Ministry spokesman Abbas Araqchi expressed hope the unrest would be resolved in a peaceful manner "with the prudence of Turkish leaders", calling it Turkey's internal issue.