US Vice President Mike Pence has moved to assure Europe the United States will back NATO even as it looks for new ways to co-operate with Russia.
However his pledge, in Munich on Saturday, has been greeted with muted applause by European allies unnerved by President Donald Trump.
In Mr Pence's first major foreign policy address for the new Trump administration, the Vice President told European leaders and ministers he spoke for Mr Trump when he promised an "unwavering" commitment to the NATO military alliance.
Mr Trump's contradictory remarks on the value of the North Atlantic Treaty Organisation, scepticism of the 2015 deal to curb Iran's nuclear ambitions and an apparent disregard for the future of the European Union have left Europe fearful for the seven-decade-old US guardianship of the West.
Mr Pence, citing a trip to Cold War-era West Berlin in his youth, said the new US government would uphold the post-World War Two order.
"This is President Trump's promise: we will stand with Europe today and every day, because we are bound together by the same noble ideals - freedom, democracy, justice and the rule of law," Mr Pence told the Munich Security Conference.
While the audience listened intently, Mr Pence received little applause beyond the warm reception he received when he declared his support for NATO.
European officials say there is still doubt about the direction of the Trump administration, particularly after US Senator John McCain told the conference on Friday the president's team was "in disarray".
Mr Pence warned allies they must pay their fair share to support NATO, noting many lack "a clear or credible path" to do so. He employed a tougher tone than Mr Trump's defense secretary Jim Mattis, who delivered a similar but more nuanced message to NATO allies in Brussels this week, diplomats said.
Mr Pence also said Russia must honour the Minsk peace accords and de-escalate violence in eastern Ukraine.