New intelligence reviewed by U.S. officials suggests that a pro-Ukrainian group carried out the attack on the Nord Stream pipelines last year, a step toward determining responsibility for an act of sabotage that has confounded investigators on both sides of the Atlantic for months.

U.S. officials said that they had no evidence President Volodymyr Zelenskyy of Ukraine or his top lieutenants were involved in the operation, or that the perpetrators were acting at the direction of any Ukrainian government officials.

The brazen attack on the natural gas pipelines, which link Russia to Western Europe, fueled public speculation about who was to blame, from Moscow to Kyiv and London to Washington, and it has remained one of the most consequential unsolved mysteries of Russia’s year-old war in Ukraine.