Explained: How the Caspian Sea could bring the Ukraine and Iran wars together

As two major wars continue to rage, a new flashpoint appears to be emerging between parties on opposite sides of the conflicts, potentially linking them in an unexpected way.

The flashpoint? The Caspian Sea, the world's largest inland body of water.

Last week, Iran summoned Ukraine's chargé d'affaires after Kyiv said it had carried out an attack in the Caspian Sea that targeted an Iranian-linked vessel. Tehran said the strike killed one sailor.

The incident has drawn attention to the Caspian Sea's growing strategic importance for both Iran and Russia, which have deepened their ties amid sweeping Western sanctions.

Ukraine last week revealed that it had struck two vessels in the Caspian Sea, saying they had departed from Iran and were heading to a Russian port.

Ukrainian President Volodymyr Zelenskyy said in a post on X that the targets included “ships that were involved in transporting military cargo from Iran, as well as a warship”, later identified as a Russian missile boat.

Iran, however, disputed Kyiv's account. It said the vessel that was hit was carrying a cargo of iron, not military equipment, and was sailing from the Russian port of Astrakhan to Iran's Anzali port, rather than the other way around.

On Monday, an Iranian foreign ministry spokesperson warned, "Ukraine's dangerous adventurism will certainly not go unanswered by us," raising concerns that the two separate conflicts could increasingly overlap if attacks on vessels in the Caspian Sea continue.

Why is the Caspian Sea important to Iran and Russia?

Bordered by Iran, Russia, Azerbaijan, Kazakhstan and Turkmenistan, the Caspian Sea has become a vital trade and logistics corridor for both Moscow and Tehran as they seek alternatives to routes affected by Western sanctions.

For Iran, the route has become even more significant due to restrictions on its access through the Persian Gulf and the Gulf of Oman.

The Caspian Sea can help Iran by allowing it to operate “a diversified trade strategy, especially if Iran promotes trade with Russia, the Caucasus, Central Asia, China via rail, and, indirectly, Eastern Europe,” as per Bijan Khajehpour, managing partner of Vienna-based Eurasian Nexus Partners, who spoke to CNN on the issue.

It is “a strategic complement rather than a substitute for Iran’s existing maritime access through the southern waters,” he added.

It was the Caspian Sea which was used to supply Moscow with Iranian Shahed attack drones during the early days of its war with Ukraine.

A 2024 report by CNN had revealed that there was reason to suspect a Russian cargo was carrying ballistic missiles from Iran to be used in the Ukraine war, and that this ship was seen in a Russian port situated on the Caspian Sea.

The US National Security Council's spokesperson, Sean Savett, had told CNN then that “any transfer of Iranian ballistic missiles to Russia would represent a dramatic escalation in Iran’s support”. And now with Ukraine directly attacking an Iranian ship in the Caspian Sea, the chances of Kyiv and Tehran coming face-to-face have just shot up.