Nato has to be good for all those involved, US Secretary of State Marco Rubio said on Friday ahead of a Nato meeting in Helsingborg, Sweden, adding that he expects the meeting will set the groundwork for the Nato leaders' summit in Ankara, Turkey, later this year.

"Like any alliance, it has to be good for everyone who's involved. There has to be a clear understanding of what the expectations are," Rubio said.

Rubio also said that a tolling system in the Strait of Hormuz by Iran would be unacceptable.