US President Joe Biden has reassured motorists that fuel supplies should start returning to normal this weekend, even as more filling stations ran out of petrol across the southeast nearly a week after a cyberattack on the nation's top fuel pipeline.
Colonial Pipeline said late on Thursday it had restarted its entire pipeline system and delivery in all markets it served. The company said it would take several days for the product delivery supply chain to return to normal along its 8850-kilometre route.
Some markets "may experience, or continue to experience, intermittent service interruptions", Colonial Pipeline said in a statement, echoing Biden who said earlier there could be "hiccups".
The pipeline, which carries 379 million litres per day of petrol, diesel and jet fuel, resumed computer-controlled pumping late on Wednesday after adding safety measures.
Petrol shortages worsened from Virginia to Florida as depots and distribution centres awaited supply.
The shutdown also forced two refineries to curb output and spurred airlines to reroute flights to refuel at airports outside the affected area. Motorists' tempers frayed as panic buying led stations to run out even where supplies were available.
The pipeline's restart should bring supplies to some hard-hit areas as soon as Thursday, US Energy Secretary Jennifer Granholm said.
On Thursday about 70 per cent of petrol stations in North Carolina were without fuel, while about 50 per cent of stations in Virginia, South Carolina and Georgia had outages, tracking firm GasBuddy said.
The average national petrol price rose above $US3 ($A3.90) a gallon, the highest since October 2014, the American Automobile Association said.
As FBI cybersleuths dug into an attack that paralysed a large part of the US energy infrastructure, the group believed to be responsible said it was publishing data from breaches at three other companies, including an Illinois technology firm.
Biden said officials did not believe the Russian government was involved in this attack.
"But we do have strong reason to believe that the criminals who did the attack are living in Russia," he said. "That's where it came from."
The website for DarkSide, the hacking group blamed for the Colonial ransomware attack, appeared to have gone offline on Thursday. The group has not returned repeated messages seeking comment through their site.
Colonial has not disclosed how much money the hackers were seeking or whether it paid.
Australian Associated Press