Police in Istanbul fired water cannons and tear gas at thousands of protesters in the city's historic Taksim Square.
Protesters converged on the site Saturday, ignoring official warnings to stay away. Organizers said they intended to march to an adjacent park that has been cordoned off by police.
The area has been a flashpoint for anti-government protests and clashes since late May, when police forcefully broke up a demonstration against a government plan to develop the park for commercial use. At least three civilians and one policeman have been killed, and many more injured, during the past month.
Protesters have focused most of their anger on Prime Minister Recep Tayyip Erdogan, who has said he will use the army to disperse demonstrations, if necessary.