Russia’s seizure of Ukraine’s naval vessels is illegal, no matter whose version of events is true, according to three international law experts who responded to questions from Defense News.

The precise events that sparked an international crisis in the Kerch Strait between Russia and its Ukrainian neighbors are hotly debated, and the two parties have opposing versions of the Nov. 25 clash. Then, Russian security services rammed, then fired on Ukrainian vessels, before ultimately seizing the ships and arresting the sailors on board.

Russia has released video confessions from Ukrainian sailors about their supposed violation of Russian sovereignty, and has put them up on charges and transferred them to prison cells in Moscow, according to Russian media reports.

Even if you take all that the Kremlin has said about the incident at face value, Russia’s actions still constitute a violation of the United Nations Convention on the Law of the Sea – a treaty that both Russia and Ukraine have ratified, experts say.

That’s the opinion of three experts from all over the globe who responded to questions from Defense News about the incident.

Julian Ku, an international law professor at Hofstra University, pointed to Article 32 of the UNCLOS treaty that delineates that warships have sovereign immunity even in another state’s territorial waters. That means “a state cannot seize a foreign warship in any circumstances, but it can expel it from its territorial waters,” Ku said.

If, as Ukraine claims and Russia disputes, the ships were conducting an innocent passage, Russia had no right to interfere with that passage, Ku said.

A Europe-based international law professor, who asked to remain on background, also via pointed to Article 30 of the UN Convention on the Law of the Sea. That language reads, “If any warship does not comply with the laws and regulations of the coastal State concerning passage through the territorial sea and disregards any request for compliance therewith which is made to it, the coastal State may require it to leave the territorial sea immediately."

“In accordance with [Article 30], even if Ukraine's warships entered into the Russian territorial sea, the Russian Federation can only require foreign warships to leave the territorial sea,” the professor wrote.

Article 32 of UNCLOS also stipulates that nothing about a country’s territorial waters affects the sovereign immunity of a warship, with the exception of the requirement to leave the waters of another state if that state finds it is in violation of innocent passage.

“Warships enjoy sovereign immunities,” the professor wrote. “Therefore, one can argue that the Russian authority cannot seize foreign warships.”

When asked via email if that reading of the treaty was in line with relevant international law, Alex Oude Elferink, director of the Netherlands Institute for the Law of the Sea, said he “would say that this is a fair summary of the situation.”

Déjà Vu

The situation in Crimea recalls the 2016 incident between the United States and Iran over an American riverine patrol’s inadvertent intrusion into Iranian waters. In that incident, lost sailors stumbled into Iranian-claimed waters around Farsi Island in the Persian Gulf – prompting Iranian forces to surround the two vessels and force them to surrender.

The incident, along with its images of American sailors surrendering on their knees and the leader of the patrol apologizing on video after less than 24 hours in captivity, was a propaganda coup for Iran’s hardliners.

But it, too, was a blatant violation of international law because Iran seized two vessels that enjoyed sovereign immunity under the UNCLOS treaty.

The United States has not formally ratified the treaty but has acceded to its provisions, which means that it abides by the treaty without subjecting itself to any international oversight. As a consequence, however, some security experts argue that the United States has diminished authority to weigh in on these issues.

Still, the U.S. Navy was incensed at the violation of international law and humiliation of its sailors at the hands of the Iranian military.

Russia has transferred the sailors to jail cells in Moscow and put them up on charges of entering Russia with weapons, which could mean up to six years in prison.

The violation of international law, and brazenness with which it has been carried out, openly flouts international norms and is a continued trampling of Ukraine’s sovereignty, said Dan Gouré, an analyst at the Arlington-based Lexington Institute.

“The seizure of these ships, just like the destabilization of Eastern Ukraine and annexation of Crimea, they are, in effect, acts of war,” Gouré said. “They are illegal and they undermine Ukrainian sovereignty.”

In the past, Russia has attempted to create pretexts for its actions – a referendum in Ukraine backing the annexation of Crimea, or backing separatists in Eastern Ukraine to create a destabilizing frozen conflict – but in this case Russia is openly acknowledging its actions. This might mean Russia has taken its campaign to a new level, Gouré said.

“The Russians are moving to new heights in their campaign against Ukraine,” he said. “And this is all part of what they want, and that is to establish a land bridge to Crimea. It’s an attempt to assert their dominance in this region, demonstrate that NATO and the U.S. are feckless, and continue the process of dominating eastern Ukraine in an attempt to absorb the region and maybe all of Ukraine.”