Fears are mounting that Russia's war in Ukraine and the war in Iran could merge into one conflict after a Ukrainian strike on an Iranian ship heightened tensions between the two regions.Tehran condemned Ukraine for carrying out the strike over the weekend on what it claims was a commercial vessel in the Caspian Sea, adding that the explosion killed one sailor and injured another.After Ukrainian president Volodymyr Zelensky acknowledged the attack, adding that the Iranian vessel was being used to transport Russian 'military cargo', Iran's foreign minister weighed in.In a post to X, Abbas Araghchi said: 'Zelensky has attacked an Iranian commercial vessel, killing a sailor.'A blatant UN Charter violation done at Israel's behest to drag Europe into its war. In calls with EU High Rep [sic] [Kaja] Kallas and [Russian] FM [Sergei] Lavrov, made clear that what the freeloader in Kyiv did CANNOT GO UNANSWERED.'Tehran decried the attack on its vessel as an act of aggression. It said it would defend its national interests and security, while accusing Kyiv of seeking to expand the war in Ukraine.It came after Zelensky said on Saturday he would share evidence with the US showing Russia is assisting Iran in targeting US bases in the Middle East through satellite surveillance.Taking to X, the Ukrainian leader wrote: 'Since the beginning of July, we have recorded active Russian satellite surveillance of the Gulf states and U.S. military facilities located there.' Navy ships of Iran and Azerbaijan move during an exercise between Iran and Azerbaijan in the Caspian Sea (File pic) Firefighters work at the site of the postal distribution centre of Nova Post company, hit by a Russian drone strike, amid Russia's attack on Ukraine