COLOMBO, Sri Lanka — Sri Lanka’s escalating political crisis turned deadly on Sunday when the bodyguard of a former cabinet minister fired on a crowd, killing at least one person and wounding two others, the police said.

The former petroleum minister, Arjuna Ranatunga, was a member of the cabinet that President Maithripala Sirisena suspended on Saturday, one day after ousting Ranil Wickremesinghe as prime minister and swearing in the former strongman Mahinda Rajapaksa.

Many lawmakers and government ministers have denounced the move as unconstitutional, and mobs have attacked government officials, deepening concerns that this island nation is headed for more turmoil.

The gunfire broke out when Mr. Ranatunga tried to enter his office at the state-run Ceylon Petroleum Corp. and was confronted by a group of workers loyal to the president. The guard opened fire, a police spokesman, Ruwan Gunasekera, said, killing one person and injuring two others, one critically. The guard was arrested.