In a statement issued late on Tuesday, Andrew Gardner, Turkey researcher at the London-based Amnesty International, censured Turkey for the recent acts of police brutality.

"Instead of continuing to repress peaceful activists, the Turkish authorities should start to look at the actions of their own police and bring to justice those responsible for the shocking abuse we have seen over the past two weeks," he said.

"The protests in Taksim Square and Gezi Park have been entirely peaceful and have a right to continue," added Gardner, who is currently in Istanbul.

Earlier in the day, Human Rights Watch issued a statement, saying Tuesday's police attack on "tens of thousands of peaceful protesters has all but destroyed efforts to foster a peaceful dialogue between the government and protesters."

"Tear-gassing tens of thousands of protesters in Taksim Square won't end this crisis," said Emma Sinclair-Webb, Turkey researcher at the New York-based Human Rights Watch.

"If Turkey is to be counted among rights-respecting countries, the police brutality has to stop and the government should talk to the protesters."

Fresh violent clashes between the police and the protesters continued throughout Tuesday, and both sides took and lost control of Istanbul's Taksim Square several times.

On Tuesday night, thousands of protesters returned to the square -- the epicenter of 12 days of unrest. Special police forces used tear gas, rubber bullets, and water cannons to disperse the demonstrators.

The unrest began on May 31 after police broke up a sit-in held at Istanbul's Taksim Square to protest against the proposal to demolish Gezi Park.

Over the next 11 days, tens of thousands of anti-government protesters held demonstrations in 78 cities across the country.

According to the Turkish Human Rights Foundation, four people have died, including a policeman, and about 5,000 people have been injured in the protests.

The protesters say Gezi Park, which is a traditional gathering point for rallies and demonstrations as well as a popular tourist destination, is Istanbul's last green public space.

Turkish Prime Minister Recep Tayyip Erdoga has been harshly criticized for the way he has handled the crisis.

According to a number of political analysts, the popularity of the ruling AK Party -- which has won three straight elections -- could decline if Erdogan does not resolve the crisis in a way acceptable to the general public.