Istanbul's prosecution office has freed 37 of 173 activists who were detained after clashes with police during the May 1 celebrations in Istanbul, Anadolu Agency reported.
Istanbul's Security Directorate's office said that the other 136 people still in custody were giving statements to the police.
The May Day protests in Istanbul were marred by violence, which saw the police use tear gas and water cannons to block demonstrators from entering Taksim Square in the city's center.
Trade unionists and other protesters, a mix of opposition party activists and some far-left groups, gathered at several locations in central Istanbul insisting on marching to Taksim Square, the scene of major anti-government protests last year, to celebrate International Workers' Day.
Istanbul's Governor Office said hundreds of activists were arrested and eight home-made bombs were seized during the day as well as other weapons, including Molotov cocktails.