Turkish police have fired tear gas and water cannon at protesters occupying a park in central Istanbul.
The protest at Gezi Park started late on Monday after developers tore up trees but has widened into a broader demonstration against Prime Minister Tayyip Erdogan.
Violence erupted after a dawn police raid on demonstrators who had camped for days in the park in anger at plans to build a shopping mall.
Clouds of tear gas rose around the area in Taksim Square, long a venue for political protest.
Broken glass and rocks were strewn across a main shopping street.
A group of primary school children ran crying from the tear gas while tourists caught by surprise scurried to get back to luxury hotels lining the square.
Riot police clashed with tens of thousands of May Day protesters in Istanbul weeks ago.
There have also been protests against the government's stance on the conflict in neighbouring Syria, a recent tightening of restrictions on alcohol sales and warnings against public displays of affection.
The Work and Pensions Secretary was today accused of misrepresenting government statistics in order to claim his cap on benefits was driving people to find work.
The Department for Work and Pensions(DWP) released figures yesterday showing the number of people expected to be hit by the cap had fallen from 56,000 to 40,000. Iain Duncan Smith hailed the figures, saying the cap had provided a "strong incentive" for people to look for jobs.
However, Jonathan Portes, the National Institute of Economic and Social Research and a former chief economist at the DWP, said "there was no evidence at all" that the cap had affected people's behaviour.
Mr Portes told the BBC Radio 4 Today programme: "It may be that the benefit cap has indeed had the effect that Iain Duncan Smith would like it to have.
"That is perfectly possible but without doing the analysis - and it has not been done - you simply cannot say that and you shouldn't say it.
"This is, I am afraid, a consistent pattern of trying to draw out of the statistics things which they simply don't show."