Speaking to reporters at Kuwait International Airport after meetings in the Gulf on Wednesday (local time), Rubio said the US security relationship with Gulf states was built on decades of cooperation and a permanent military presence rather than promises alone.

"So we don't... We have existing relationships with these countries that go back many, many decades. We have troop presence in these countries. We have assets in these countries," Rubio said.

"I didn't sense any doubts about our security assurances, because they're real. They're not promises; they're actual. They exist."

Rubio said Washington would remain closely aligned with Gulf partners as negotiations with Iran continue following the memorandum of understanding reached in Switzerland.

"We're going to be completely aligned with our partners in the Gulf," he said.