"It is part of a larger campaign… to contain Russia globally… Of course, it is unacceptable and it is not what an ambassador should be doing, it is in fact the opposite of that", Zakharova told the TV channel Rossiya 1.
German media reported last week that Richard Grenell had written letters to companies involved in the project that seeks to bring Russian natural gas to Europe across the Baltic Sea, saying they faced a significant risk of sanctions.
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European Commissioner Guenther Oettinger said in December that construction was already underway and no US threats could stop the project.
The United States has adopted a provision that allows it to sanction countries involved in the project to bring 1.9 trillion cubic feet of gas annually across the Baltic Sea, bypassing Ukraine.