Turkish riot police backed by water cannon faced off with about 1,000 trade union workers in the capital Ankara on Monday, after a weekend of some of the worst clashes since anti-government protests erupted late last month.
Police officers used megaphones to order workers to stop their march towards Ankara's central Kizilay district.
"Those of you on the streets must stop blocking the streets. Do not be provoked. The police will use force," they shouted, as several water cannon were positioned a few hundred meters away.
Further marches by striking workers were planned in Istanbul on Monday, despite government warnings that demonstrations would not be tolerated.
"There is an attempt to bring people to the streets through strikes and work stoppages. These will not be allowed," Interior Minister Muammer Guler told reporters.
Prime Minister Tayyip Erdogan is seeking to restore calm after weekend unrest during which police fired teargas and water cannon to clear thousands of protesters from around Taksim Square in Istanbul, the focal point of the demonstrations.
Police detained 441 people in connection with clashes in Istanbul on Sunday and 56 in the capital Ankara. As violence across several cities entered its 18th day, at least four people have been killed and around 5,000 injured, according to the Turkish Medical Association.
What began as a small demonstration by environmentalists upset at government plans to build on a public park adjoining Taksim has grown into a movement against Erdogan, who opponents say is overbearing and meddles too much in their personal lives.
"We are tired of protesting, we don't want to keep doing this, we want to return to our lives - but we are tired of this oppressive government constantly interfering," said Mahmet Cam, a teacher among the striking workers in Ankara.
There were also clashes on Monday in the city of Eskisehir, around 200 km southeast of Istanbul, where police used teargas and water cannon to disperse crowds and cleared away hundreds of tents, the Dogan news agency reported.
European Union enlargement commissioner Stefan Fuele expressed concern about developments in Turkey, whose negotiations to join the bloc have sputtered partly over worries about its record on human rights and freedom of speech.
"Turkey needs de-escalation and dialogue, not continuation of excessive use of force against peaceful protesters. We watch with concerns," he tweeted.
Germany has long harbored doubts about admitting Turkey to the EU. Chancellor Angela Merkel said she was "appalled, like many others" shocked at Turkey's tough response to the protests.
"I would like to see those who ... have a different opinion and a different idea of society having some space in a Turkey that moves into the 21st century," she told the German broadcaster RTL.
"What's happening in Turkey at the moment is not in line with our idea of the freedom to demonstrate or freedom of speech."
Erdogan sought to seize the initiative over the weekend by holding huge rallies in Istanbul and Ankara. Hundreds of thousands turned up to support a leader who has won three successive elections, whom they considered unfairly under siege.
While the unrest has not posed a serious threat to his 10-year rule, it presents the greatest public challenge to the leadership of a man who has guided Turkey to economic prosperity and relative stability on the fringes of a volatile Middle East.
The blunt-talking 59-year-old said the rallies were to kick off campaigning for local elections next year and not related to the unrest, but they were widely seen as a show of strength.
A defiant Erdogan told a sea of flag-waving supporters in Istanbul on Sunday that the unrest had been manipulated by "terrorists" and dismissed suggestions that he was behaving like a dictator, a constant refrain from protesters on the streets.
Just a few kilometers away, police fought running battles with protesters in clashes that lasted well into the evening.
The stark contrast between events in different parts of Istanbul highlighted how the protests have polarized Turkey, its conservative religious heartland largely backing Erdogan while Western-facing liberals swell the ranks of the protesters.
Investors have been spooked by the demonstrations, although Turkey's currency, stocks and bonds recovered to pre-protest levels by Friday. On Monday, however, assets were down again.
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