Has the door closed on diplomacy between Iran and US?

Iranian president calls new US sanctions against Tehran 'idiotic and dangerous.'

'The White House has lost its mind.'

That's how Iran's president Hassan Rouhani described the latest round of US sanctions against his country.

The new measures target Iran's Supreme Leader and his military chiefs, denying them access to financial resources.

The sanctions are designed to punish Tehran for what the US calls its destabilising activities in the Middle East, and prevent it from developing nuclear weapons.

But Iranian leaders say Washington has closed the door on diplomacy.

So, do sanctions work? And what's needed to break this cycle of escalating rhetoric between the two sides?