A deadly Ukrainian attack on a key strategic lake that Russia and Iran use to smuggle arms threatens to tear open a new front that could dramatically expand the war.

Ukraine said its drones hit a Russian missile boat, oil platform and two sanctioned military cargo vessels in the Caspian Sea late last month. (Iran claims Ukraine struck a commercial cargo ship, killing a sailor, and threatened retribution.)

The strike prompted fears of a fusing of the two ongoing conflicts, one launched by Vladimir Putin and the other by Donald Trump.

Tehran claimed that the attack aimed to bring Europe into the Middle East war and said it was considering retaliating by striking one of Ukraine’s ports with a ballistic missile, according to The New York Times.

Andrii Sybiha, Ukraine’s foreign minister, called Iran’s claims “lies” and branded the regime a “direct accomplice to Russian aggression against Ukraine”. Iran ultimately backed down, with its foreign minister saying Sybiha had assured him the attack “was unintentional and Ukraine seeks no escalation”.