US Vice President Mike Pence also called on European allies to carry their share of the burden, saying "the promise of sharing the burden of our defence has gone unfulfilled by too many for too long and it erodes the very foundation of our alliance."
US Vice President Mike Pence on Saturday reassured Europe that the United States would back NATO.
The vice president told European leaders and ministers at the Munich Security Conference that he spoke for President Donald Trump when he promised an "unwavering" commitment to the NATO military alliance.
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.
"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," Pence told the conference.
European officials speaking to reporters in Munich said there was 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."
Pence warned allies they must pay their fair share to support NATO, noting many lack "a clear or credible path" to do so.
German Chancellor Angela Merkel warned countries not to retreat from the international cooperation which she says is the only way to solve global problems.
"In a year in which we see unimaginable challenges we can either work together or retreat to our individual roles. I hope that we will find a common position," she said.
This includes working not only with Western partners, but also with Russia if possible and if Moscow once again respected the sovereignty and territorial integrity of other states such as Ukraine, she said.
She said it was "regrettable" that Europe had not managed to reach a stable relationship with Russia over the last 25 years.
"I will not give up on finding a way for better relations with Russia despite our different views on many questions," she said.
TRT World's Simon McGregor-Wood brings us the latest from Munich.