Turkish police fired tear gas and water cannon at hundreds of stone-throwing May Day protesters on Friday, after they defied a ban and tried to march on Istanbul's Taksim Square.
Europe's biggest city was under a security lockdown as thousands of police manned barricades and closed streets to stop demonstrations at Taksim, a traditional rallying ground for leftists that saw weeks of unrest in 2013.
Riot police unleashed water cannon and chased protesters down side streets in the nearby Besiktas neighborhood and also they also fired off canisters of tear gas, a Reuters reporter said. Demonstrators lobbed stones and bottles at police and set off fireworks.
Istanbul police said nearly 140 people had been detained, although activists said the number was nearly double that. The city's governor said 6 police officers and 18 protestor had been injured in clashes, which died out as the afternoon wore on and a clean-up operation got underway.
Critics say President Tayyip Erdogan and the government have become more authoritarian in the buildup to June elections.
"People want to express their problems but the government doesn't want those problems to be heard ahead of elections," opposition politician Mahmut Tanal, holding a pocket-sized book of the Turkish constitution, told Reuters in Besiktas.
A usually bustling square lined with cafes and hotels, Taksim was filled with police buses, ambulances and satellite broadcast trucks. A pair of tourists emerged from a hotel to find the area sealed off and nervously made their way around police lines.
Much of Istanbul's public transport had been shut down due to security concerns, and police helicopters buzzed over the city. Tens of thousands also gathered to march in the capital Ankara, where the mood was more festive, with dancing and singing.
The government had said Taksim would only be open to those who came peacefully and not for "illegal demonstrations".
"I wish May 1 to be celebrated in a festive mood without provocations," Erdogan said in a statement.
Opposition parties and unions called on the government to lift the ban.
Erdogan has previously dismissed protesters as "riff-raff" and terrorists, outraged by the 2013 unrest that brought unwanted international attention and posed the biggest challenge to his AK Party since it came to power in 2002.
Recent polls say AKP is on course for another election win in June but he may fall short of the massive victory Erdogan is targeting to allow him to change the constitution and bolster his presidential powers.
The 2013 Taksim protests began as a peaceful demonstration against plans to redevelop Gezi Park, a leafy corner of the square. After a police crackdown the demonstration spiraled into weeks of nationwide protests against Erdogan's rule.