Sri Lanka's new prime minister will begin forming a unity government on Friday, but his appointment has failed to appease anti-government protesters demanding the resignation of the president for the country's disastrous economic crisis.

President Gotabaya Rajapaksa appointed veteran opposition politician Ranil Wickremesinghe as the island nation's prime minister late on Thursday after a week of violent clashes that left nine people dead and over 300 injured.

The president's elder brother, Mahinda Rajapaksa...