Corruption-related losses at Brazil's state-run oil firm Petrobras will likely surpass 20 billion reais (US$5.3 billion), federal prosecutor Deltan Dallagnol said Oct. 9.

Dallagnol, part of a task force overseeing Brazil's largest-ever corruption investigation, said the 6.2 billion reais ($1.6 billion) in corruption-related losses the company wrote off in April was "just the tip of the iceberg."

In April, Petrobras also wrote down another 44.6 billion reais ($11.8 billion) of assets. While the additional charges reflected falling oil prices and a weaker Brazilian currency against the dollar, they were also sparked by refineries and other facilities whose value was inflated by the corruption scandal.

Prosecutors have accused executives at the nation's top engineering firms of forming a cartel to fix contracts and overcharge Petrobras for work, using the excess to line their own pockets, bribe politicians and finance election campaigns.

Dallagnol, speaking at an event in Rio de Janeiro, said the more than 20 billion reais estimate includes outright losses as well as illicit profits that the engineering firms earned through price fixing and overcharging.