The State Department submitted a report to the U.S. Congress listing two vessels and an entity, Transadria Ltd., involved in the pipeline, Blinken said, but did not give details on the second vessel.

Washington opposes the $11 billion pipeline, which runs under the Baltic Sea to bypass Ukraine and carry gas from Russia's Arctic region to Germany.

Nord Stream 2 has faced stiff opposition from the United States and some European states, which say it will make Europe too reliant on Russian gas. But other European governments say the link is vital to secure energy supplies, with gas prices surging in recent weeks and the threat of power outages looming this winter.

The Biden administration has waived sanctions on the pipeline's operator and reached an agreement with Germany in July over the pipeline. Germany agreed to take action if Russia uses energy as a weapon in its relations with Ukraine, but the pact did not provide a specific criteria for how that would be judged.

Last week, Germany's energy regulator temporarily halted the certification process for the new pipeline that will carry Russian gas into Europe, throwing up a new roadblock to the contentious project and driving up regional gas prices.

"Even as the administration continues to oppose the Nord Stream 2 pipeline, including via our sanctions, we continue to work with Germany and other allies and partners to reduce the risks posed by the pipeline to Ukraine and frontline NATO and EU countries and to push back against harmful Russian activities, including in the energy sphere," Blinken said.

Ukraine will lose revenues if gas from Russia bypasses it and it accuses Moscow of using energy as a weapon to threaten Europe's security.

(Reporting by Daphne Psaledakis, Timothy Gardner and Andrea Shalal in Washington; Additional reporting by Kanishka Singh in Bengaluru; Editing by Sonya Hepinstall and Sandra Maler)