SAO PAULO: Shares in Brazilian state oil company Petrobras plunged Monday after President Jair Bolsonaro changed the company's chief executive, fueling fears he will try to block further energy price hikes as he eyes re-election.

The company's ordinary and preferential shares both dived by more than 19 percent shortly after opening on the Sao Paulo stock exchange, which was pulled down more than five percent overall.

Bolsonaro on Friday appointed army reserve general Joaquim Silva e Luna as president of Petrobras, shortly after saying that "people can't be surprised" by the firm's price increases.

Petrobras has increased fuel prices four times so far in 2021, a cumulative rise of nearly 35 percent, as global oil prices have recovered to pre-coronavirus pandemic levels.

"The government has clearly showed interference in Petrobras, because Bolsonaro is openly against the system of floating fuel prices," said economist Alex Agostini of credit rating firm Austin Rating.

"It's a clear signal he's going to intervene on prices. And we know when that's been done in the past under (former president) Dilma Rousseff, it led to very big losses for Petrobras," he told AFP.

Shares in state electricity company Eletrobras were down eight percent amid fears the far-right president would also target electricity prices as he gears up his bid to win re-election in 2022.

The Brazilian real fell more than 2.5 percent against the dollar.