The Biden administration on Sunday declared a state of emergency in response to a ransomware attack that forced operator Colonial Pipeline to shut down a key U.S. pipeline.

Why it matters: Friday night's cyberattack is "the most significant, successful attack on energy infrastructure" known to have occurred in the U.S., notes energy researcher Amy Myers Jaffe, per Politico.

• It follows other significant cyberattacks on the federal government and U.S. companies in recent months.

The big picture: Colonial Pipeline carries 45% of fuel supplies in the eastern U.S. Some 5,500 miles of pipeline has been shut down in response to the attack.

• While gasoline and diesel prices aren't expected to be impacted if pipeline operations resume in the next few days, fuel suppliers are becoming "increasingly nervous" about possible shortages, Bloomberg notes.

What's happening: Department of Transportation issued the declaration to keep fuel supply lines open.

• It said in a statement the declaration "addresses the emergency conditions creating a need for immediate transportation of gasoline, diesel, jet fuel, and other refined petroleum products and provides necessary relief."
• Colonial said in a statement Sunday while its main fuel lines remained offline, some smaller lines between terminals and delivery points were now operational.

What they're saying: Commerce Secretary Gina Raimondo told CBS' "Face the Nation" there's an "all hands on deck" effort to resume operations.

• "We are working closely with the company, state and local officials, to make sure that they get back up to normal operations as quickly as possible and there aren’t disruptions in supply," she told CBS' John Dickerson.