The United States is as committed to NATO as ever but demands that European allies spend substantially more on defence, US Secretary of State Marco Rubio said on Thursday, while adding that the US would give allies some time to do that.

Rubio spoke as he met fellow NATO foreign ministers gathered in Brussels, with Europeans hoping he would dispel doubts about the US stance even with tensions rising over President Donald Trump's steep new trade tariffs.

The Trump administration’s words and actions have raised questions about the future of NATO, the transatlantic alliance that has been the bedrock of European security for the past 75 years.

“The United States is in NATO ... The United States is as active in NATO as it has ever been,” Rubio told reporters, dismissing doubts about that commitment as “hysteria”.

Rubio added that Trump was “not against NATO. He is against a NATO that does not have the capabilities that it needs to fulfil the obligations that the treaty imposes upon each and every member state.”

Trump has said the military alliance should spend 5 percent of gross domestic product on defence – a huge increase from the current 2 percent goal and a level that no NATO country, including the United States, currently reaches.

Washington has also bluntly told European countries that it can no longer be primarily focused on the continent’s security.

European allies have been anxiously seeking details on the timeframe and extent to which the US aims to reduce its engagement in NATO for weeks, in order to coordinate the process of a European defence ramp-up to avoid security gaps in Europe.

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In Brussels, Rubio brought some element of response on that.

Among the economies hit by US President Donald Trump’s sweeping tariffs announced on Wednesday: some remote Australian islands that are home to penguins, but not people, and a tiny outpost 600 miles off eastern Australia.

“We do want to leave here with an understanding that we are on a pathway, a realistic pathway, to every single one of the members committing and fulfilling a promise to reach up to 5 percent of spending,” he said, adding that this included the United States.

“No one expects that you’re going to be able to do this in one year or two. But the pathway has to be real.”

European ministers are expected to use the meeting to showcase their plans to boost defence spending.

According to NATO estimates, 23 of the alliance’s 32 members met or exceeded the 2 percent target last year. Some of the continent’s big economies, such as Italy and Spain, were among those below the target, at around 1.5 percent and 1.3 percent respectively.

European ministers are also likely to use the meeting to try to influence the talks Trump has initiated with Russia over the war in Ukraine, which was triggered by Moscow's 2022 invasion.

European belief in the US as the continent’s ultimate protector against any attack from Russia has been severely shaken by Trump’s attempted rapprochement with Moscow and heavy pressure on Kyiv as he seeks to end the war.