WASHINGTON- U.S. environmental regulators issued an emergency fuel waiver on Tuesday to help alleviate any shortages in reformulated gasoline in the Mid-Atlantic states as supplies tighten five days after a cyberattack shuttered the nation's biggest pipeline.

The Environmental Protection Agency said the fuel vapor rule waiver would continue through May 18 for fuel sold in Washington, D.C., Maryland, Pennsylvania and Virginia, and that it may take other steps along with the Department of Energy (DOE).

The White House in a statement late on Monday also said it was continuing to monitor supply shortages and was evaluating its options following the Colonial Pipeline attack.

"EPA and DOE are continuing to actively monitor the fuel supply situation resulting from the Colonial Pipeline shutdown and considering additional measures to alleviate the impact," it said in a statement.

On Sunday, the U.S. Transportation Department said it was issuing a temporary hours of service exemption for truck drivers transporting gasoline, diesel, jet fuel and other refined petroleum products in states that could be impacted by the pipeline shutdown.

The hack of the Colonial Pipeline shut down a major artery to ship fuel along the eastern United States, although the company has said it expects to get the pipeline back in service by the end of this week. 

(Reporting by Susan Heavey and David Shepardson; Editing by Doina Chiacu and Paul Simao) ((sheavey@thomsonreuters.com; +1-202-843-6292;))