WASHINGTON—The Department of Homeland Security on Tuesday announced new requirements for U.S. pipeline operators to bolster cybersecurity following a May ransomware attack that disrupted gas delivery across the East Coast. In a statement, DHS said it would require operators of federally designated critical pipelines to implement “specific mitigation measures” to prevent ransomware attacks and other cyber intrusions. Operators must also implement contingency plans and conduct what the department calls a “cybersecurity architecture design review.” It’s the latest response by the Biden administration to a series of ransomware attacks and intrusions hitting critical U.S. infrastructure and raising fears about American cybersecurity. DHS did not immediately release further details about the guidance, which comes after another directive issued weeks after the May 7 attack on Georgia-based Colonial Pipeline. That attack led to the shutdown of a system delivering about 45 percent of the gasoline consumed along the East Coast and sparked long …