The Washington Post reported that ransomware was used in the attack, citing two U.S. officials it didn’t identify. It wasn’t clear if the attack was carried out by foreign government hackers or a criminal group, the officials told the Post.

In ransomware attacks, hackers typically encrypt an organization’s computer files and then demand a ransom payment to unlock the data.

Colonial, which runs the largest U.S. gasoline and diesel pipeline system, has hired a third-party cybersecurity firm to investigate and contacted law enforcement and other federal agencies. It’s trying to minimize disruption to customers, the company said in a statement late Friday.

The company didn’t immediately respond to a phone call or email for further comment Saturday.

Officials at the Federal Bureau of Investigation, the Department of Justice and the Department of Homeland Security’s Cybersecurity & Infrastructure Security Agency didn’t immediately respond to requests for comment.

Hacking threats to critical infrastructure have been growing, prompting the White House to respond with a plan to try to increase the security of utilities and their suppliers.

The first leg of that effort, announced April 20, will address security holes in the electrical grid, before moving to other sectors, including the country’s gas pipelines and water utilities.

Pipelines are a growing concern because they play a central role in so many parts of the U.S. economy. The Colonial artery can transport 2.5 million barrels a day of refined petroleum products from the Gulf Coast to Linden, New Jersey. It supplies gasoline, diesel and jet fuel to fuel distributors and airports from Houston to New York.

Nymex gasoline futures rose 1.32 cents to settle at $2.1269 per gallon Friday in New York.

–With assistance from Michael Riley and Ben Bain.