Iranian officials have ramped up their threats towards Kyiv after this weekend’s attack by Ukraine on an Iranian vessel in the Caspian Sea, the route for much of the country’s trade with Russia.

Three crew members were injured and one seafarer killed aboard the ship, Iran’s regional governor Hadi Hagh-Shenas said on Sunday.

The vessel had been carrying a cargo of iron and was sailing from Astrakhan to Anzali, “a safe and reliable corridor for commercial exchanges between the two ports,” Hagh-Shenas said.

“Any attack on Iran always comes with a cost, and that remains true today; the U.S. and Israel are well aware of this,” the head of the Iranian parliament’s national security, Ebrahim Azizi, wrote on X. “Ukraine, too, may soon come to understand that Iran does not let actions go unanswered.”

Iran’s foreign minister, Seyed Abbas Araghchi, also lashed out at Ukraine’s leader, Volodymyr Zelensky.

“Zelenskyy 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,” wrote on X Sunday. “What the freeloader in Kyiv did CANNOT GO UNANSWERED.”

Some background: Ukraine on Saturday said it had struck ships in the waterway that were transporting military goods from Iran to Russia.

Ukraine had “achieved very good results from long-range strikes in the Caspian Sea,” Zelensky said in a post on X.

“Specifically, these include ships that were involved in transporting military cargo from Iran, as well as a warship,” Zelensky said.

Iranian officials have said that the United States has also recently attacked facilities on the Caspian Sea. The Gilan governorate announced an airstrike on an Islamic Revolutionary Guard Corps navy.