Three employees were injured on Sunday in an explosion at an oil refinery operated by Brazil's Petrobras, Reuters reported.

One worker suffered 75 percent burns on his body while another two suffered less serious burns in the blast.

"The injured were quickly tended to by refinery medical personnel and taken to hospital. The company is providing the necessary assistance," Petrobras said in a statement.

The state-run oil company declined to say on Monday whether oil processing or fuel output at the 323,000-barrels-a-day Landulpho Alves Refinery (RLAM) near the northern city of Salvador had been affected by the accident, Reuters reported.

But the company said in a statement that fuel supplies to customers would not be disrupted.

Petrobras has started an investigation into what caused the explosion. Simão Zanardi, a spokesman for FUP, Brazil's national oil workers' federation, told Reuters that the injured workers had been using an electric rotary sander on the inside of a hydrogen tank that had been drained several days earlier and where workers had already done the same work without incident.

The explosion on Sunday followed a fire in the paraffin unit at RLAM last Wednesday after a faulty valve leaked kerosene. No injuries resulted from that incident.

Petrobras refines about 2.1 million barrels of oil per day in its Brazilian refineries, which have been operating near full capacity in an effort to meet rapidly rising domestic demand.