President Gotabaya Rajapaksa ordered the three-day deployment to maintain order in the central town of Rambukkana, where police dispersed a demonstration with live rounds and tear gas on Tuesday.

A 42-year-old man was shot dead in Tuesday's melee and nearly 30 others were wounded.

"To ensure there are no incidents during and after the burial, President Gotabaya Rajapaksa invoked public security provisions," Sri Lanka's information department said in a statement.

The military "will assist the police in maintaining public order" until Saturday, it added.

Police violently broke up the Rambukkana protest after a crowd blocked a railway line and highway connecting the capital Colombo with the central city of Kandy to protest oil shortages and high prices.

A curfew imposed in Rambukkana was lifted on Thursday, but heavily armed police were seen patrolling the streets.

A judicial inquiry into the shooting is under way.

Sri Lanka is suffering its most painful economic downturn since 1948, with months of lengthy blackouts and acute shortages of food, fuel and other essentials causing widespread misery.

Protesters have demanded Rajapaksa step down over the government's mismanagement of the crisis, and a large crowd has been camped outside his seafront office in Colombo since April 9 to call for his resignation.