US President Donald Trump has urged Nato allies to commit 4% of their annual output (GDP) to military spending – double the current target.
The White House confirmed he had made the remarks during the Western military alliance’s summit in Brussels.
Earlier, Mr Trump criticised Germany over its defence spending and energy reliance on Russia.
Nato’s secretary-general said the main focus should be on all members reaching the current target of 2% of GDP.
Jens Stoltenberg declined to answer a specific question about Mr Trump’s remarks, but told reporters: “I think we should first get to 2%, focus on that now… the good thing is that we are moving to that.”
For decades after the end of the Cold War, he said, Nato countries had cut defence budgets as tensions fell – and now needed to increase them at a time when tensions were rising.
Previous US presidents have urged Europe to take more responsibility for their defence and reduce the burden on US taxpayers of maintaining forces in Europe long after the end of the Cold War – but none as bluntly as Mr Trump.
In a statement, White House spokeswoman Sarah Sanders said: “During the president’s remarks today at the Nato summit he suggested that countries not only meet their commitment of 2% of their GDP on defence spending, but that they increase it to 4%. The president raised this same issue when he was at Nato last year.
“President Trump wants to see our allies share more of the burden and at a very minimum meet their already stated obligations.”
The Brussels meeting comes less than a week before Mr Trump is due to hold his first summit with Vladimir Putin, in Helsinki, reviving concerns among US allies over his proximity to the Russian president.
President Trump shocked some by quipping that the Nato summit might prove harder than the Putin talks.
What is the spending row about?
Mr Trump’s main objection is that all but a handful of member states have still not increased their defence budgets to meet a goal of spending at least 2% of their annual economic output on defence by 2024.
Of Nato’s 29 members, just five meet that target this year: the US, Greece, Estonia, the UK and Latvia.
However, several, such as Poland and France, are close to the mark.
The Nato alliance was set up in 1949 to counter the Soviet Union, of which Russia is the main successor state.
Is Trump committed to Nato?
By Jonathan Marcus, BBC defence and diplomatic correspondent
So is this mission accomplished at Nato for Donald Trump? Has he achieved his goal of persuading his European allies to spend more on defence?
He began the day by calling them “delinquents” and ended it with smiles. The Nato communique contained the usual words about “turning a corner” in terms of defence spending, while recognising “the need to do more”.
How much more and how quickly still remains an issue, with Mr Trump suggesting that the benchmark Nato spending goal of 2% of GDP devoted to defence should be doubled to 4%. That is a level that all the allies apart from the US would struggle to attain.
But the real underlying issue remains Mr Trump’s commitment to Nato. Does he see it merely as a set of transactional relationships, or as an organisation enshrining the transatlantic partnership that has been the central element of European and US security since World War Two?
Mr Stoltenberg has sought to play down Mr Trump’s accusations, saying he expected Nato leaders would agree they were “stronger together than apart”.
He also tried to separate arguments about trade – not a primary Nato concern – from discussions about military matters.
“There are disagreements on trade. This is serious. My task is to try to minimise the negative impact on Nato,” Mr Stoltenberg told a forum on the sidelines of the summit.
At the G7 summit in Canada last month, German Chancellor Angela Merkel led efforts to reach agreement with Mr Trump on trade but the American leader rejected the G7 summit joint communique after he left.
What did Trump say about Germany?
Mr Trump clashed with Mrs Merkel ahead of the summit.
Germany has the EU’s biggest economy and has long been accused by US administrations of failing to contribute its fair share to Nato operations but Mr Trump’s comments were particularly stinging.
The US president accused Germany of only spending “a little bit over 1%” of its economic output on defence compared to the 4.2% spent by the US “in actual numbers”.
Germany spends 1.24% of GDP on defence and the US 3.5%, according to the latest Nato estimate.
At a breakfast meeting in Brussels with Mr Stoltenberg, the US leader also said: “Germany is totally controlled by Russia because they will be getting from 60% to 70% of their energy from Russia, and a new pipeline, and you tell me if that’s appropriate because I think it’s not and I think it’s a very bad thing for Nato.”
EU figures suggest Russia is responsible for between 50% and 75% of Germany’s gas imports, but gas makes up less than 20% of Germany’s energy mix for power production.
Germany has given political support for a new Baltic Sea pipeline, Nord Stream 2, which will increase the flow of Russian gas to EU states.
Mr Trump later made more conciliatory remarks on Wednesday after he and Mrs Merkel met on the sidelines of the Brussels summit, saying defence spending and trade had been discussed.
“We have a very, very good relationship with the chancellor. We have a tremendous relationship with Germany,” Mr Trump said.
How did Merkel respond?
She hit back, comparing German independence now with the time when she grew up in the former East Germany, a satellite of the then Soviet Union.
Mrs Merkel told reporters: “I am very happy that today we are united in freedom as the Federal Republic of Germany. Because of that we can say that we can make our independent policies and make independent decisions. That is very good, especially for people in eastern Germany.”
She added that Germany had put a huge proportion of its troops at Nato’s disposal.
“We are still very heavily involved in Afghanistan and thus we also defend the interests of the United States of America… and Germany was pleased to do it and did it out of conviction,” she said.
Mrs Merkel said she had discussed migration and trade with Mr Trump, and that she looked forward to further discussions as the US and Germany remained partners.