Bangkok: Singapore's squeaky clean image has taken a battering as the city-state's leaders come to grips with its largest ever corruption scandal that engulfed oil rig builder Keppel Offshore and Marine.

Senior Minister for State Finance and Law Indranee Rajah insists the company, a unit of the government-linked conglomerate Keppel Corporation, has not got off "lightly" by agreeing to pay a $US422 million ($536 million) fine to avoid a criminal trial in the US for bribing Brazilian officials.

Crew members walk on board a floating liquefaction vessel built by Keppel Offshore and Marine. Credit:Bloomberg

"As far as the company is concerned, make no mistake, there has been a heavy price to pay, and deservedly so," Indranee told Singapore's Parliament in the first comments on the scandal by a government leader.

Singapore has been known for years as the least corrupt nation in Asia and last year moved up a notch to be ranked the world's seventh least corrupt nation by Transparency International.