My assumption is that given that Iran is doing this, not Russia, it’d be more likely for a response to be against Iran. Russia isn’t really the one escalating – they’ve already been firing all the ballistic missiles that they can get their hands on at Ukraine and obviously would accept missiles if they show up at their door. It’s Iran who is escalating.
We also explicitly stated that we would act if Iran did this.
US threatens ‘swift and severe’ response if Iran sends ballistic missiles to Russia
“As our partners have made clear … we are prepared to deliver together a swift and severe response if Iran were to move forward of the transfer of ballistic missiles, which would in our view represent a dramatic escalation in Iran’s support for Russia’s war of aggression against Ukraine,” he continued.