The Nato secretary-general tried to dampen fears yesterday that the US would pull thousands of troops out of Germany as the alliance faces an increasingly belligerent Russia.
"It's not yet decided how and when this decision will be implemented," Jens Stoltenberg said in Brussels, after Donald Trump confirmed reports of a cut of more than 9,000 troops, down from 34,000 to around 25,000.
"The US presence in Europe is not only about protecting Europe, but it's also about protecting US power beyond Europe," he told the US president.
Mr Trump branded Germany, a Nato ally, "delinquent" on Monday for not meeting a goal set in 2014 for members to halt budget cuts and move toward spending at least 2pc of gross national product on defence by 2024.
Defence ministers from the alliance will discuss Mr Trump's plans to cut troops based in Germany, a hub for US operations in the Middle East and home to its European command headquarters, by a third during video talks today and tomorrow.
The United States, which will retain 50,000 military personnel in Europe, may use the meeting to brief allies on the decision for the first time, two Nato diplomats said.
The defence ministers will also sign off on a package of measures against Russia, including military exercises and bulk buying of air defences after Moscow illegally beefed up its missile arsenal.
Britain and the US are leading the push, which will remind Moscow of their nuclear arsenal and bring transatlantic security under a new "umbrella" for the first time in the alliance's 71-year history.
Sources described the move as "a significant step forward".
Within German politics, only the opposition Free Democrats say Berlin should have done more to appease the Trump administration by increasing its military budget to the 2pc target agreed upon by Nato.
"The transatlantic partnership has become a form of blackmail," warned Left Party leader Dietmar Bartsch, adding that Berlin should now drop its commitment to the Nato defence spending target. Johann Wadephul, an MP for the ruling CDU, said "the actions and their justification are wrong and will weaken Nato. Germany is strengthening its defence capabilities even during the corona crisis".
Emily Haber, Germany's ambassador to the US, said: "US troops... are not there to defend Germany. They are there to defend trans-Atlantic security. They are also there to project American power in Africa, in Asia."
Ben Hodges, a retired US general who commanded American army forces in Europe, described it as a "colossal mistake".
"If they go through with it, the damage to the relationship between Germany and the United States would be significant," he told Reuters.