ISTANBUL — The Turkish authorities widened their crackdown on the antigovernment protest movement on Sunday, taking aim not just at the demonstrators themselves, but also at the medics who treat their injuries, the business owners who shelter them and the foreign news media flocking here to cover a growing political crisis threatening to paralyze the government of Prıme Minister Recep Tayyip Erdogan.

After an intense night of street clashes that represented the worst violence in nearly three weeks of protests, Mr. Erdogan rallied hundreds of thousands of his supporters on Sunday — many of them traveling on city buses and ferries that the government had mobilized for the event — at an outdoor arena on the shores of the Sea of Marmara. In some of his toughest language yet, he called his opponents terrorists and made clear that any hope of a compromise to end the crisis was gone.

“It is nothing more than the minority’s attempt to dominate the majority,” he said of the protesters. “We will not allow it.”

The escalating tensions have raised the risk of an extended period of civil unrest that could undermine Turkey’s image as a rising global power and a model of Islamic democracy, which Mr. Erdogan has cultivated over a decade in power.