Ukraine’s drone strike on an Iranian cargo ship in the Caspian Sea last weekend has escalated tensions between the two countries and highlighted the growing links between the separate conflicts they’re fighting. Iran has vowed to respond to Saturday’s attack, which it said was against a commercial vessel and killed a sailor. Ukraine claimed the vessel was carrying military equipment between Iran and Russia.Ukrainian Foreign Minister Andrii Sybiha said Tuesday he called his Iranian counterpart Abbas Araghchi for “a frank discussion” and stressed the need to “avoid unnecessary escalation.”“Our goal is to counter Russian aggression, which is the root cause…