ISTANBUL—Turkish antigovernment demonstrations widened Saturday as more than 100,000 protesters took to the streets in cities across the country, forcing Prime Minister Recep Tayyip Erdogan to withdraw riot police from Istanbul's landmark Taksim Square.

But the prime minister, making his first comments on the protest since Wednesday, also struck a defiant tone, labeling his detractors "a minority," and calling on them to cease the protests.

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