Turkish riot police have moved into Istanbul's Taksim Square, which has been occupied by anti-government protesters for close to two weeks.
Officers fired tear gas and rubber bullets, leading many protesters to flee the square into adjoining Gezi Park, where many have been camping.
Some activists responded by hurling fireworks, fire bombs and stones at police.
The unrest began after a police crackdown on a protest over Gezi Park.
The protests then widened, with demonstrators accusing Mr Erdogan's government of becoming increasingly authoritarian and trying to impose conservative Islamic values on a secular state.
The move into the square by police comes after Prime Minister Recep Tayyip Erdogan agreed to meet the protest organisers on Wednesday.
Backed by armoured vehicles, officers wearing helmets and carrying shields gathered around the square early on Tuesday before moving past barricades erected by protesters.
They removed protesters' banners which had been hung from a building overlooking the square.
Istanbul Governor Huseyin Avni Mutlu said the police had no intention of breaking up the protest in Gezi Park.
"Our aim is to remove the signs and pictures on Ataturk statue and the Ataturk Cultural Centre. We have no other aim," he wrote on Twitter. "Gezi Park and Taksim will not be touched."
A similar message was broadcast by police via loudspeaker, but protesters in the square said they did not believe this.
The BBC's Mark Lowen, who is in the square, says this was a deliberate show of force that may jeopardise Wednesday's talks.
The demonstrations are now in their 12th day, with activists controlling much of Taksim Square.
The unrest was sparked after police moved to suppress environmental protests over the redevelopment of Gezi Park on 31 May.
Three people have died and more than 5,000 have been injured since the protests began.
Smaller protests have occurred in the capital Ankara too. Police there have used water cannon and tear gas to break up demonstrations almost every night.