A constitutional crisis gripping Sri Lanka since the president's shock dismissal of Prime Minister Ranil Wickremesinghe erupted into violence Sunday, with a man shot dead and two others injured in Colombo.

Police said bodyguards for a Sri Lankan cabinet minister allied to Wickremesinghe opened fire inside a government ministry as a mob loyal to President Maithripala Sirisena besieged the minister's office. Three people were injured but a 34-year-old man died shortly after.

It was the first fatality since Sirisena sacked Wickremesinghe on Friday and installed a former strongman as prime minister, triggering political chaos in the Indian Ocean nation.

Wickremesinghe has refused to vacate the prime minister's official residence, barricading himself inside as over 1,000 supporters, including chanting Buddhist monks, rallied outside.

The 69-year-old says his sacking is illegal, and wants an emergency session of parliament held to prove he still commands a majority.

Sirisena shut parliament for nearly three weeks to forestall any challenge to his appointment of Mahinda Rajapakse, a former president accused of wartime abuses.

Rajapakse sought blessings at a prominent Buddhist temple Sunday as he jostled to consolidate his claim to the prime ministership.

But Wickremesinghe got a boost as Sri Lanka's parliamentary speaker refused to endorse his sacking.