According to local reports, 25,000 police have been deployed at Istanbul’s Taksim Square, the epicenter of the 2013 rallies.
PM Recep Tayyip Erdogan earlier urged youths to not join Saturday’s protests.
Protests against plans to redevelop Gezi Park in Istanbul turned into mass rallies against PM Recep Tayyip Erdogan last year after a heavy-handed police response.
A number of people were killed in the unrest, with thousands more injured.
Clashes broke out in Istanbul on Saturday after protesters marched on Taksim Square despite a government ban on gatherings in force there.
Riot police, water cannon and armored vehicles were deployed to block access to the square and nearby Gezi Park. A number of demonstrators have also reportedly been arrested.
Security forces also fired tear gas at demonstrators in central Ankara.
Earlier on Saturday, Istanbul officers kicked and detained a CNN reporter during a live broadcast from Taksim Square.
Ivan Watson said in a Twitter post that he and his film crew were “released after half an hour”.
The main organizers behind last year’s Gezi Park protests – Taksim Solidarity – had called for a demonstration to mark the one-year anniversary.
Rallies were also expected to take place in several other Turkish cities, including Izmir and Antakya.
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