The planned Nord Stream 2 gas pipeline from Russia to Germany raises U.S. intelligence and military concerns since it would allow Moscow to place new listening and monitoring technology in the Baltic Sea, a senior U.S. official said on Thursday.

Sandra Oudkirk, Deputy Assistant Secretary of State for Energy Diplomacy, said in Berlin that she would meet German officials to voice Washington's concerns about the subsea project, as reported by Reuters.

A consortium of western companies and Russia's Gazprom said this week it was starting preparatory work on the project off Germany's Baltic coast.

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Oudkirk told reporters that the U.S. Congress had given the president new authorities to impose sanctions against a variety of Russian pipeline projects.

Any companies involved in such projects were in "an elevated position of sanctions risk", she said. However, she added that Washington was focused on using diplomatic means to halt Nord Stream 2, one of several Russian projects to export gas to western Europe via routes avoiding Ukraine, with which Moscow is involved in a series of disputes.

Oudkirk said Washington's objections included past Russian moves to turn off gas supplies to Ukraine and other countries, adding that it perpetuate "vulnerabilities" in Russian-European ties for another 30 to 40 years.

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The United States also opposes the TurkStream land pipeline that would run through Turkey for the same reasons, she said.

She said the Baltic was a congested, sensitive military area. "When we look at the ability of governments and companies to use infrastructure deployments as a means to convey devices and technologies that can listen and follow and monitor, that is a concern with regard to this particular undersea pipeline project in the Baltic Sea."

"The new project would permit new technologies to be placed along the pipeline route and that is a threat," she said.

Oudkirk rejected speculation that Washington was opposing the pipeline to help U.S. liquefied natural gas exports.

The Nord Stream 2 project has said it will tap banks for financing in the fourth quarter of 2018 or early next year.

Denmark must still rule whether the pipeline can be built near its coast, and other routine permissioning processes are still under way in Sweden and Russia.

Oudkirk said Washington supported a Danish-Polish Baltic Pipe pipeline project because it would diversify sources and routes. The project, to be built by 2022, is Poland's flagship project aimed at reducing reliance on Russian gas.

Gazprom's Western partners are energy companies Uniper , Wintershall, Engie, Austria's OMV and Anglo-Dutch group Shell.