America's top diplomat levelled his latest criticism as he headed to a meeting of the military alliance in Sweden.
US President Donald Trump has fiercely criticised NATO members for not doing more to help the US-Israeli military campaign. He has said he is considering withdrawing from the alliance and questioned whether Washington was bound to honour its mutual defence pact.
NATO officials have stressed the US did not ask the 32-member alliance to take part in the Iran war, but many members have honoured commitments to allow US forces to use their airspace and bases on their territory.
There have also been tensions over the response of the UK and other NATO countries to the crisis in the Strait of Hormuz, which was open to shipping prior to the US and Israel offensive against Iran.
Washington has argued Europe needs the sea route "much more than we do" and ensuring free transit of vessels was "much more their fight than ours".
Rubio would not be drawn over reported plans by the US to reduce its force contribution to the alliance, insisting it was a matter for the president and defence department.
But he said: "I don't think anyone is shocked to know that the United States, and the president in particular, is very disappointed at NATO right now."
While a long-time supporter of the alliance, Rubio said the refusal by members, such as Spain, the use of their bases, made the US question the benefit of membership.
"Understand that there are many countries in NATO that agree with us that Iran can't have a nuclear weapon, that Iran is a threat to the world.
"So the president said, 'fine, I'm going to do something about it'.
"He's not asking them to commit troops. He's not asking them to send their fighter jets in. But they refuse to do anything.
"So, I think the president looks at that and says, hold on a second, if all these countries around the world agree with us that Iran can't have a nuclear weapon and this regime is a threat to world peace and security, that already have missiles that can reach Europe - they don't have missiles that could reach America yet, but they have missiles that could reach Europe - we're actually stepping forward to do something about it, and everyone goes into hiding."
European concerns about Trump's attitude toward NATO were also exacerbated this year by his push to acquire Greenland, a territory of fellow NATO member Denmark.
At the meeting in the Swedish town of Helsingborg, European ministers are expected to try to placate the US by stressing they are ready to help with freedom of navigation in the Strait of Hormuz when conditions permit and to take more responsibility for European security. Iran has restricted traffic through the strait during the war.
European fears about the US president's commitment to NATO have been heightened by the decision to withdraw 5000 troops from Europe, which US officials linked to German Chancellor Friedrich Merz's criticism of Trump's Iran war strategy.
with Reuters
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