Unrest gripped Turkey again last night as tens of thousands of anti-government protesters took to the streets of Istanbul, and police answered them with tear gas, water cannon and clubs.

In Taksim Square, unarmed protesters tried to stop an advancing water cannon truck – at one point even trying to hold it back with their arms. Another protester brandished a handful of carnations at the driver, as if in rebuke. Across the square, a tearful woman angrily asked police why they had attacked protesters again. A police officer pushed her violently aside. A man tried to stand still, in a new tactic adopted by protesters, but riot police, their shields up, pushed him to the ground before one started beating him when he tried to stand up again.

Half an hour before, Taksim Square had been peaceful. A huge crowd had massed, carrying red carnations in memory of at least four people killed in the protests so far. In a good-natured protest they had chanted, "Everywhere is Taksim, everywhere is resistance," and called on Mr Erdogan's government to resign.

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Then, in a blaze of colour, they had thrown their carnations in the air. It was an eloquent gesture: they had answered the brutal crackdown on earlier protests with flowers. Some carried Brazilian flags in acknowledgement of protests sweeping Brazil. For a moment, it seemed as if they had reclaimed Takism Square.

But the peaceful atmosphere was not to last. The police began ordering the protesters to disperse. Over a loudspeaker, an officer told them they had made their point. Some began to drift off, but others did not want to go. Then the police began to advance in lines, forcing the protesters back across the square while water cannon fired indiscriminately into the crowd. There was no sign of violence from any of the protesters in the square.

The crowd returned to the square repeatedly and a stand-off developed at the junction with Istiklal Street, one of the city's main nightlife areas. Meanwhile police were chasing other protesters through the surrounding back streets, crowded with tourists and locals out for Saturday night. Police fired huge amounts of tear gas in the narrow streets and large clouds of it were seen billowing over the city. There were unconfirmed reports they had also used rubber bullets.

Mr Erdogan continues to refuse to answer the protesters' demands. Instead, he is touring Turkey, addressing mass rallies of his AK Party supporters, in a show of force. Hours before the protest in Taksim Square, he spoke to a crowd of around 15,000 in the Black Sea port of Samsun, saying: "One prayer from our people is enough to frustrate their plans".

In what seemed an attempt to provoke religious anger, he repeated earlier claims the protesters had defiled mosques and attacked head-scarved women; there is no evidence they did either. A photograph alleged to show a protester drinking alcohol in a mosque turned out to show him drinking Coca-Cola and there were head-scarved women among the protesters in Taksim.

The renewed violence comes after a few days in which protesters had stayed away from the square, instead holding meetings in city parks to decide what to do next in their campaign against Mr Erdogan. As the tear gas drifted across Istanbul, the two sides appeared further apart than ever.