Russia’s attack on Ukrainian naval vessels in the Black Sea was a violation of international law and a dangerous escalation of the undeclared war the Kremlin has waged for more than four years against Ukraine in Crimea, in the breakaway provinces of eastern Ukraine, and now at sea.

The Kremlin can shout all it wants about a provocation, about an attempt by the Ukrainian president to create a political diversion or about anything else, but none of that changes the fact that Russia had no legal justification for firing on three Ukrainian boats and seizing them.

The vessels, two small armored boats and a tugboat, were headed for the Kerch Strait, which separates Crimea from Russia and is the only entrance to the Sea of Azov, where much of Ukraine’s coastline lies . Russia claimed they had crossed into Russian waters, but that is based on its illegal claim to Crimea, which it seized in 2014.

Ukraine and most every other state in the world still regard Crimea and its coastal waters as Ukrainian territory. And under a treaty ratified by Ukraine and Russia in 2004 — a now hard-to-imagine time when they could still refer to each other as “historically brotherly nations” — the Azov Sea and the Kerch Strait were defined as shared territorial waters. That treaty, signed by President Vladimir Putin of Russia, is still in force.