US Assistant Secretary of State Sandra Oudkirk said that Washington could consider retaliatory measures within the framework of Countering America's Adversaries Through Sanctions Act.
During the meeting with German Chancellor Angela Merkel on April 27, Trump offered to refuse from the support of the gas project in the exchange for new trade agreements between the USA and the EU.
Any companies involved were in "an elevated position of sanctions risk", she said.
The German government's point man for Russia, Dirk Wiese, said that at a time of strong disagreements between Russia and the West over Ukraine and other matters, Berlin views the pipeline and the Iran deal as "islands of cooperation" with Moscow.
The Thirsk and Malton MP said: "Despite the fact oil and gas exports make up 70% of Russia's global trade, these are not now covered under the European Union sanction regime due to the high reliance of the European Union on Russian gas exports".
Oudkirk said the US also opposed the pipeline due to security concerns, adding it would allow Russian Federation to place listening devices along the pipeline's route, although she declined to comment on specific devices.
"The new project would permit new technologies to be placed along the pipeline route and that is a threat".
The United States also opposes the Turkish Stream offshore pipeline that would bring Russian gas via the Black Sea to Turkey for the same reasons, she said.
Jens Mueller, a spokesman for Nord Stream 2, dismissed concern that the new pipeline would create more dependence on Russian gas, saying it would be only one of many sources of natural gas for Western Europe.
US President Donald Trump plans to promote US liquefied natural gas (LNG) exports at a meeting next Thursday (6 July) in Warsaw with a dozen leaders from Central and Eastern Europe, a region heavily reliant on Russian supplies.
As previously reported "FACTS", the President of Ukraine Petro Poroshenko warned Germany from participating in the construction of the "Nord stream-2", proposing as an alternative to the modernization of the transit pipeline passing through the territory of Ukraine.