Nearly 600 people have been arrested in Istanbul as police launched a dramatic clampdown on left-wing demonstrators trying to hold a May Day rally.
Officers fired tear gas and used batons to stop the crowd marching to Taksim Square, where they were due to mark the 30th anniversary of "Bloody May Day".
Thirty-four people died in 1977 after a gunman fired, triggering a stampede.
This year's rally is taking place in a country already tense over a disputed presidential election.
The constitutional court is currently examining an opposition call to cancel the election of Foreign Minister Abdullah Gul as president. The first round of parliamentary voting ended in disarray on Friday.
After some violent clashes in one area of the city, a handful of trade union leaders were allowed into the square to lay red carnations in memory of those who died in 1977.
But police stopped television crews setting up satellite dishes in the square - one channel did however film events from a nearby building.
Meanwhile, public transport was paralysed, as the authorities sealed off main roads, cancelled ferries and closed underground stations
Although the march was not specifically linked to the ongoing tension over the election, correspondents say some protesters raised their fists and called for the resignation of Prime Minister Recep Tayyip Erdogan - who supports Mr Gul as president.
The presidential election has pitted secularists against the Islamist-rooted AK party, which has an overwhelming majority in parliament.
The army - seen as a guardian of Turkish secularism - has warned that it will defend the separation of state and religion, the legacy of the state's founder Mustafa Kemal Ataturk.
Mr Erdogan, the AK leader, appealed for national unity in a televised address to the nation on Monday.
On Sunday, hundreds of thousands of people rallied in Istanbul in support of secularism in Turkey.