June 11, 2013 -- Protesters in Turkey's ancient city of Istanbul fought running battles with police today, sending fireworks into police lines while being forced back with tear gas, rubber bullets and water cannon.

Earlier police had forced their way past improvised barricades to clear Taksim Square of protesters who had been occupying the area for the past 12 days in protest at the rule of Prime Minister Recep Tayyip Erdogan. The protests have become the biggest test of his decade of power.

The protests have swelled from a peaceful demonstration into nationwide disturbances that have spread to 78 cities across the country. Demonstrators are challenging what they say is the prime minister's increasingly authoritarian style and his perceived attempts to impose a religious and conservative lifestyle in a country with secular laws.

Earlier in the day, Erdogan had made it clear that he had come to the end of his patience with the protesters, vowing to "end the actions" of the demonstrators, accusing them of damaging Turkey's image abroad.

During the afternoon, many of the protesters in Istanbul had fled into the adjacent Gezi Park, where hundreds have been camping out to stop developers from cutting down trees in the park.

Police moved in, while bulldozers began demolishing the barricades and the makeshift shelters. The clashes that followed saw police and protesters take and lose control of the square several times.

As night fell, massive plumes of tear gas billowed upward, and police fired water cannons. Thousands of defiant demonstrators swarmed back into Taksim Square, and were met by lines of riot police. Amid a violent game of cat and mouse, fires burned, protesters set off fireworks, threw stones and waved banners while water cannons drenched protesters, including a man in a wheelchair carrying a Turkish flag.

Unrest continued into the night as the mayor of Istanbul promised the authorities would continue "day or night to clear the square of marginal elements." Before the evening clashes, more than 300 people had been treated in a makeshift infirmary set up in a park at the center of the protest. Most were suffering from the effects of tear gas.

Turkey is one of the United States' key allies. Two weeks ago, Erdogan visited the White House and was hailed by President Obama as a friend of America. The president said the visit "reflected the importance of the partnership" he had been able to develop with Erdogan as an ally against Syria, and against Iran developing a nuclear weapons program. But in recent days, the United States has expressed "serious concerns" about what it described as "excessive use of force by police.

Four people, including a policeman, have died in two weeks of demonstrations. The Turkish Human Rights Foundation says around 5,000 people have been treated for injuries or the effects of tear gas.