If struck first, one is justified in striking back with similar force. Indeed, it is likely a necessity lest the world see not striking back as a sign of weakness.
But certainly announcing this is entirely a result of internal Iranian troubles.
There is an historiographical theory called "Primacy of Domestic Politics". The idea is that foreign policy is a reflection of domestic politics. When things are bad internally, the foreign policy will attempt to take attention away from internal disputes and focus attention outside.
This can be applied to the outbreak of WWI. Neither Germany, Austria nor Russia wanted war. At any point any one could have stopped it before it started. They sent telegraphs to each other pleading for someone else to stop it. But all three had serious internal trouble. So, none did. Because a war against a foreign rival shifts attention away from internal disputes to a unifying crusade against an opponent.
And 37 million people died in the fighting and of the effects of fighting, among them the royal family of one of the three main instigators.
But it doesn't necessarily have to result in war, of course. Some general tension can be enough.