Public Security Minister Raul Jungmann pledged hefty fines against distribution firms supporting the strike to protest diesel price hikes, which has emptied roads and left major cities running short on food, gasoline and medical supplies.

Highway blockades and fuel shortages have also halted industries from automaking to sugarcane crushing, hammering exports of everything from beef and soybeans to coffee and cars.

"Starting today, we will begin to find those infiltrators and we will fine those companies," he said in a radio interview, adding that antitrust agency Cade would also investigate the fuel distributors involved. "They know the price they will pay for the suffering they have imposed on the Brazilian people."

The more aggressive stance underscored the government's mounting urgency to end a nationwide protest that his been slow to unwind despite a raft of concessions that President Michel Temer offered over the weekend.

Some factions within the loosely organized trucker movement have added to demands and ignored a call to demobilize by industry group Abcam, which spearheaded the early protests and says it represents 600,000 drivers.

Oil industry regulator ANP said fuel distribution had begun to improve in cities such as Rio de Janeiro and the capital Brasilia but it remained scarce in several regions including the business hub of Sao Paulo.

It will take at least a week for fuel distribution to return to normal, according to ANP.