COLOMBO, Sri Lanka — President Mathripala Sirisena of Sri Lanka on Saturday suspended Parliament for two weeks as he sought to shore up support for unseating the country’s prime minister, escalating a political crisis.

Mr. Sirisena suspended Parliament after ousting Prime Minister Ranil Wickremesinghe on Friday, a move many lawmakers and government ministers denounced as unconstitutional. Mr. Sirisena swore in as prime minister Mahinda Rajapaksa, a popular former president who was accused of human rights abuses and corruption during a decade in power.

Mr. Wickremesinghe struck a defiant tone, asserting that he was still prime minister. “Convene Parliament, and I will prove it,” he said.

By Saturday afternoon, many lawmakers were vowing to stick by Mr. Wickremesinghe, demanding that a formal count be taken in Parliament to determine who held a majority in the house. That’s when Mr. Sirisena announced that he was suspending Parliament. He also dismissed the leaders of several government institutions, replacing them with loyalists.