Up to now, the Trump administration has merely threatened to impose sanctions on any company assisting with the construction of Nord Stream 2 on the floor of the Baltic.  During the past several weeks, as construction on the last few kilometers has begun despite the threats, the U.S. government has set out to demonstrate that it is not a paper tiger, in other words that it is ready to carry out the threats.

The U.S. source said the State Department is expected to issue a report by Thursday or Friday on companies it believes are helping the Russia-to-Germany pipeline. Companies that could be in the report include ones providing insurance, helping to lay the undersea pipeline, or verify the project's construction equipment, the source said.

Zurich Insurance Group could be listed in the report, the source said, though Zurich said it is "committed to fully comply with any applicable sanctions regulations." And German companies like Uniper, BASF's Wintershall, Anglo-Dutch oil major Shell and Austria's OMV could all be on the punitive target list.