NATO foreign ministers are set to continue consultations on Friday in the Swedish port city of Helsingborg with talks focused on expanding Europe's military capabilities.
US Secretary of State Marco Rubio, who is set to join the meeting, repeated his criticisms of European allies before leaving for Sweden on Thursday.
There is anger in the administration over the refusal of countries such as Spain to allow the use of bases for the war against Iran, he said. The US membership in an alliance had to have value for the US and that a central value in NATO was US bases in Europe.
If then you have "countries like Spain denying us the use of these bases, well then why are you in NATO. That's a very fair question," Rubio said in an interview that was shared on YouTube.
He did say that "other countries in NATO have been very helpful," though he did not name them, but said the situation needs to be discussed.
The Trump administration is also putting pressure on Europe to drastically increase defence spending and to assume more responsibility for Europe's defence.
The talks in Helsingborg are meant to prepare for an upcoming summit of the alliance in Ankara in July.
NATO Secretary General Mark Rutte has said that Washington could announce changes in its contributions to the alliance's force planning.
Earlier this month, US announced the withdrawal of around 5,000 troops from Europe and decided not to implement plans to deploy medium-range weapons in Germany for now.
The talks on Friday follow a dinner on Thursday evening which was attended by Sweden's King Carl XVI Gustaf and Queen Silvia focused on continued support for Ukraine.
