"The president's views of, frankly, disappointment at some of our NATO allies and their response to our operations in the Middle East are well documented," Rubio said on Friday at a gathering of NATO foreign ministers in the Swedish town of Helsingborg.
"That will have to be addressed. That won't be solved or addressed today. That's something for the leaders level to discuss," Rubio told reporters, adding that any alliance "has to be good for everyone who's involved".
It was his first meeting with NATO allies since the war on Iran sparked deep divisions inside the bloc, with Trump saying he was considering withdrawing from the alliance and questioning whether Washington was bound to honour its mutual defence pact.
NATO allies reacted with relief to Trump's turnabout that came after weeks in which the president fiercely criticised NATO members for not doing more to help the US-Israeli military campaign.
"Good alliances are those based on cooperation, mutual respect, and a commitment to our shared security," Polish President Karol Nawrocki wrote on X after Trump had cited his relationship with Nawrocki as the reason behind his decision.
The move confirms that Polish-American ties are "very strong, and Poland is a model ally", Defence Minister Wladyslaw Kosiniak-Kamysz wrote on X.
Poland's Foreign Minister Radoslaw Sikorski said US troop numbers in his country would now remain at "more or less the previous level," which Kosiniak-Kamysz specified to be about 10,000 personnel.
Earlier, Polish authorities had been alarmed by reports that the Pentagon had cancelled plans for the rotational deployment of some 4000 US troops there. It was not immediately clear where the additional 5000 fresh troops would come from.
"It's confusing," Sweden's Foreign Minister, Maria Malmer Stenergard noted when asked about the back and forth in the deployment saga.
Rubio said the pledge of extra troops demonstrated that "the United States continues to have global commitments that it needs to meet in terms of our force deployment" but cautioned deployments would continue to be re-examined.
He did not spell out in public any US plans to cut Washington's commitments to NATO's defence plans, a topic meant to be discussed the same day at NATO's Brussels headquarters, according to sources.
European concerns about Trump's attitude towards NATO were also exacerbated by Trump's push to acquire Greenland, a territory of fellow NATO member Denmark, and the cancellation of the planned deployment of long-range Tomahawk missiles to Germany.
At the meeting in Helsingborg, NATO allies again stressed their commitment to step up and take their fair share of the burden, both in securing the freedom of navigation in the Strait of Hormuz when conditions permit and in Europe's defence.
"We recognise that there is a desire to draw down the troop numbers ... What is important is that it happens in a structured manner," Norway's Espen Barth Eide said.
He was echoed by his Dutch counterpart Tom Berendsen.
with Reuters
