US Secretary of State John Kerry said a speech by Iranian Supreme Leader Ali Khamenei on Saturday vowing to defy American policies in the region despite a deal with world powers over Tehran's nuclear programme was "very disturbing".

"I don't know how to interpret it at this point in time, except to take it at face value, that that's his policy," he said in the interview with Saudi-owned Al Arabiya television, parts of which the network quoted on Tuesday.

"But I do know that often comments are made publicly and things can evolve that are different. If it is the policy, it's very disturbing, it's very troubling," he added.

Ayatollah Khamenei told supporters on Saturday that US policies in the region were "180 degrees" opposed to Iran's, at a speech in a Tehran mosque punctuated by chants of "Death to America" and "Death to Israel".

"Even after this deal our policy towards the arrogant US will not change," Khamenei said.

Several Gulf Arab states have long accused Tehran of interference, alleging financial or armed support for political movements in countries including Bahrain, Yemen and Lebanon.

Kerry said the US believed its Arab allies had the ability to confront Iranian interference in the region.

"I think President Obama's belief and our military assessments, our intelligence assessments, are that if they organise themselves correctly, all of the Arab states have an untapped potential that is very, very significant to be able to push back against any of these activities," he said. – Reuters