COLOMBO, Sri Lanka — Sri Lanka’s politics plunged into deeper turmoil on Friday when a majority of the country’s parliamentarians refused to recognize the appointment of the new prime minister amid rising tensions and accusations of millions of dollars in bribes.

Last week, President Maithripala Sirisena unexpectedly fired Prime Minister Ranil Wickremesinghe, accusing him of being inflexible and corrupt, and replaced him with Mahinda Rajapaksa, a former president who is considered by many to be the strongman of Sri Lankan politics. Human rights investigators have accused Mr. Rajapaksa of war crimes dating to the country’s civil war.

Since last week both Mr. Rajapaksa and Mr. Wickremesinghe have claimed to hold power, setting off a constitutional crisis in this island nation, a popular tourist destination and a major producer of tea and coconuts.

While Mr. Rajapaksa has been meeting with foreign diplomats and making the rounds of government offices in the seaside capital, Colombo, Mr. Wickremesinghe has been holed up in the stately prime minister’s residence, Temple Trees. Hundreds of his supporters are standing guard outside, vowing to protect him.