Rubio says Gulf talks were 'frank' as US seeks regional backing

US Secretary of State Marco Rubio has declined to reveal what concerns Gulf leaders raised during meetings on his regional tour, saying only that the discussions were candid and constructive.

Speaking to reporters, Rubio said Washington had "very frank" conversations with its longstanding allies as it sought their views on the US-Iran agreement and wider regional issues.

"That's what we're here to do, get their input," Rubio said. "I thought they were very frank, honest and important conversations, and I think we're very strongly aligned."

Rubio is visiting Bahrain, Kuwait and the UAE, where discussions have centred on the memorandum of understanding with Iran and security in the Strait of Hormuz.