Iran says that the weakest scenario in itself will cause a "historic nightmare"
That has seen US futures turn flat while bond yields have also eased to session lows at the moment. In turn, that has brought USD/JPY down to a low of 108.26 but all in all, I would say that the reaction has been rather mild.
Iran has been warning about retaliation over the past few days but so far all we're hearing is one threat after another with little action to show for.
I reckon markets won't be too disheartened by that and the longer this goes on, market participants will become more accustomed to the rhetoric. Unless Iran really does take military action, I doubt markets will be too negatively impacted by the headline earlier.