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A Reuters reporter saw protesters escaping into side streets after police used water cannon and tear gas. Shops rolled down their shutters.
Smaller demonstrations also took place in the coastal city of Izmir and in the capital Ankara, where about 300 protesters chanted slogans opposing the government and the internet bill.
The bill would give the courts the power to rule on removing material from the internet that "violates individual rights", an article that opponents say is murky and could lead to the arbitrary closure of websites.
It also says that people will be able to apply to the state Telecommunications Directorate (TIB) as well as the courts to block material that "violates the secrecy of private life".