Washington: Donald Trump's tweets on Saturday accusing Germany of owing the United States "vast sums of money" for NATO have been rejected, with the German Defence Minister questioning the US president's understanding of NATO finances.

Ursula von der Leyen on Sunday called the criticism "inaccurate," without mentioning the president by name.

"NATO does not have a debt account," Ms Von der Leyen said in a statement released by her ministry.

In reality, NATO has only a small logistical budget, which relies on funding by all member states. The vast majority of NATO members' total resources are managed domestically.

Ms Von der Leyen's response to Mr Trump's tweets – made less than 24 hours after a meeting with German Chancellor Angela Merkel – echoed other experts, including former US ambassador to NATO Ivo Daalder.

"Trump's comments misrepresent the way NATO functions," Mr Daalder told The Washington Post.

"The president keeps saying that we need to be paid by the Europeans for the fact that we have troops in Europe or provide defence there, but that's not how it works."

Ms Von der Leyen also indirectly criticised Mr Trump's plan to reduce funding for UN peacekeeping missions.

German defence expenditure was not exclusively dedicated to NATO missions, she emphasised, and additional German funding would be used for UN peacekeeping missions.

"What we want is a fair burden-sharing, and in order to achieve that we need a modern understanding of security," she said.

The rather unusual rebuke of Mr Trump by a German defence minister indicates growing concerns in Berlin over trans-Atlantic relations.

The percentage of Germans who view the United States as a trustworthy ally has dropped from 59 per cent in November to 22 per cent in February. In recent months, Sigmar Gabriel, Germany's outspoken vice-chancellor and foreign minister, has even called Mr Trump a "threat."

This is a shift in a nation that has long considered itself one of the United States' closest allies, although at times an uncomfortable one.

Germany's foreign policy is still shaped by memories of World War II, and foreign military operations are deeply unpopular with German voters. Instead of boosting its defence spending, Germany has historically invested more in development aid and deepened its economic ties with other nations.

But Germany is also the largest European host nation for US troops, home to about 30,000 American service members. Theoretically, Mr Trump could threaten to withdraw some of those troops and move them elsewhere, but such a move would make little strategic sense for the United States, which relies on its military bases in Germany for operations in eastern Europe and the Middle East. Over the past decade, US bases in Germany have mostly benefited America.

Mr Trump's tweets won't make it any easier for Ms Merkel to persuade a wary German public to increase military funding.

During her meeting with Mr Trump on Friday, Ms Merkel explicitly reaffirmed her commitment to nearly double Germany's defence spending until 2024, but that plan still needs to be approved by her government and Parliament.

If passed, the increase would meet NATO's requirement that member states spend 2 per cent of GDP on defence by 2024, a goal set three years ago.

Germany currently pays 1.2 per cent; the United States kicks in more than 3 per cent. Four other countries – Greece, Estonia, Poland and Britain – also meet their obligation.

Germany would find itself under more pressure to increase military funding if those four other nations backed Mr Trump's criticism.

"Nobody in Estonia wants to be left out in the cold because Germany doesn't spend enough money on defence," said Marcel Dirsus, a German security politics scholar, referring to fears of a Russian invasion in Estonia.

The Washington Post