"We've expressed our opposition to this deal and the influence it will actually give Russia. But we're not going to let that issue get in the way of a tremendous relationship that we have with the country of Germany," he said during a visit to Berlin, AFP reported.
"We're going to continue to work with Germany and the rest of the allies in the region to strengthen our alliances and continue to move forward."
Germany has long irked allies with its stubborn defense of the Nord Stream 2 project.
The 10-billion-euro ($11-billion) pipeline beneath the Baltic Sea is set to double Russian natural-gas shipments to Germany, Europe's largest economy.
The United States and several European countries are deeply opposed to the project, arguing that it will increase German and EU dependence on Russia for critical gas supplies.
The pipeline also avoids Ukraine, depriving Kiev of gas transit fees.
US President Joe Biden's administration has also signaled that it was committed to complying with an anti-Nord Stream law providing for sanctions which was passed in 2019 under his predecessor Donald Trump, who had from the start taken a combative approach to Germany.
Despite the intense pressure, Germany has not budged from the project, which it says ensures a more stable and cleaner source of energy as it pivots away from coal and nuclear power.