ISTANBUL, June 15 (Reuters) - Turkish riot police stormed a central Istanbul park on Saturday firing tear gas and water cannon to evict hundreds of anti-government protesters, hours after an ultimatum from Prime Minister Tayyip Erdogan.

Lines of police backed by armoured vehicles sealed off Taksim Square in the centre of the city as officers stormed the adjoining Gezi Park, where protesters had been camped in a ramshackle settlement of tents.