The nuclear issue and Iran's desire to expand its influence in the Middle East are Washington's main concerns, US Secretary of State Marco Rubio said.

"Suffice it to say that the nuclear question is the reason why we’re in this in the first place.  If Iran was just a radical country run by radical people but – it would still be a problem, but they are revolutionary.  In essence, they seek to expand and export their revolution, not just what they do in Iran – that’s why they’re with Hezbollah in Lebanon and that’s why they supported Hamas, that’s why they supported the militias in Iraq.  They don’t just seek to dominate Iran, they seek to dominate the region.  And imagine that with a nuclear weapon," Rubio said in an interview with Fox News.

According to the US Secretary of State, Tehran currently has “half the missiles,” which puts it in a weak position.

Asked by the reporter about US measures in the event of a failure to reach an agreement with Iran, Rubio said the main approach would be to increase pressure on Tehran.

“(...) the level of sanctions on Iran are extraordinary, the pressure on Iran is extraordinary, and I think more can be brought to bear,” he said.

Rubio noted the US believes Iran’s new Supreme Leader, Mojtaba Khamenei, is alive, but there are doubts that he has “the same credibility as his father did.”

“We don’t know the answers to these questions and – but I certainly think that there’s dysfunction in their [i.e. Iran’s] system, which is making it harder to negotiate with them right now,” the top US diplomat added.