"From our perspective, it's very hard to see gas flowing through the pipeline or for it to become operational if Russia renews its aggression on Ukraine," U.S. Deputy Secretary of State Wendy Sherman told reporters in Brussels after a meeting of the NATO-Russia Council.

The pipeline, which is not yet operational, undermines the energy security and the national security of a "significant part of the Euro-Atlantic community", she said.

(Reporting by Robin Emmott, John Chalmers and Sabine Siebold)