U.S. President Joe Biden on Thursday raised his concerns to German Chancellor Angela Merkel over the Nord Stream-2 gas pipeline project, warning Russia not to weaponize the energy.

The 1,230-km gas pipeline, which is expected to be completed next month, would bring natural gas from Russia to Germany through the Baltic Sea.

"I reiterated my concerns about Nord Stream-2," Biden told reporters at a press conference after their meeting, adding that "Merkel and I are absolutely united in our conviction that Russia must not be allowed to use energy as a weapon to coerce or threaten its neighbors."

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The United States has long claimed that the project was a geopolitical maneuver by Russia that will undermine Ukraine's role in transiting energy to Europe. 

Kremlin has described the project as largely commercial, saying there was no need for political discussions. Germany, too, points out that the project is purely commercial.

The United States and Germany have different assessments regarding the Nord Stream-2, Merkel said at the conference, while stressing both agree that Ukraine will remain a transit country for natural gas.

"We will be actively acting should Russia not respect this right of Ukraine that it as a transit country," she added via translation. "The Nord Stream-2 is an additional project and certainly not a project to replace any kind of transit through Ukraine."

Citing the importance of relations with Germany and the difficulty in stopping the nearly completed pipeline, the Biden administration in May waived sanctions against a company behind the pipeline project and its German CEO, which led to opposition from bipartisan lawmakers.

"By the time I became president, it was 90% completed, and imposing sanctions did not seem to make any sense," Biden said on Thursday. He noted the two allies instead will look at practical measures to ensure European energy security will not be weakened by Russian actions.

The two leaders also covered topics such as climate change, the COVID-19 pandemic, and Iran nuclear issue.

Biden expressed condolences to Merkel over the  loss of life due to the flooding in Germany that has left 58 people dead and dozens missing.

Merkel is the first European leader to visit the White House since Biden took office. The visit was widely seen as an effort to restore the relationship between Washington and Berlin, which had been damaged by his predecessor Donald Trump.

It is likely Merkel's last official trip to Washington as she will step down following elections in September after 16 years in office.

(With input from Xinhua)