NATO's latest moves could bottle up much of Russia's naval power

Since midnight Wednesday, Moscow time, Russia has been warning the world that any ship approaching a Ukrainian port "will be regarded as potential carriers of military cargo."

This obvious threat to sink commercial shipping appears to be an attempt to prevent ships from taking on Ukrainian grain. This week, Russia unilaterally ended talks on renewing the Black Sea Grain Initiative that has allowed food to flow to other countries from Ukraine, despite the war.

Ukrainian President Volodymyr Zelenskyy has asked Turkey to join him in a new arrangement to protect grain ships without Russia's involvement. Turkey has yet to respond.

The threat to sink commercial shipping marks an escalation that can only be carried out under a state of declared war, said Tanya Grodzinski, a naval historian at the Royal Military College in Kingston, Ont. That's something Russian President Vladimir Putin has been anxious to avoid, opting instead to present his war on Ukraine as a "special military operation."

The new threat may say more about Russia's weakness than its strength, as the strategic balance in the waters around European Russia shifts against it.

The day the NATO summit in Vilnius opened — July 11 — was marked in Cuba by the arrival of the Russian Navy warship Perekop of the Baltic Fleet.

The Cuban government welcomed the Perekop — the biggest Russian warship to visit Cuba in many years — with a cannon salute from Havana's old fort.

For Moscow, the visit allowed Russia to project its military power into the Americas and show support for the Cuban Communist Party, a close ally, on the second anniversary of a popular revolt against its rule.

But as the fanfare unfolded in Havana, events in Vilnius that morning and the night before were building a new fence around the Perekop's home ports of St Petersburg and Kaliningrad. Russia's Baltic fleet will still be able to sail in peacetime but it's being strategically bottled up as its home sea becomes a NATO lake.

And to the south, Russia's storied Black Sea fleet, already hurt by the humiliating loss of its flagship Moscow, faces an uncertain future and the possible loss of both its bases and its naval supremacy.

The Baltic and the Black Sea share a geographical feature: they both have only one slender opening into the world's oceans.

In the Baltic, three narrow straits separate Denmark from Sweden; the widest, between two Danish islands, is a mere 16 kilometres across.

Ships seeking to exit the Black Sea to enter the Mediterranean must sail the Bosphorus River and the Dardanelles Strait — both of which are entirely within the territorial waters of NATO member Turkey.

Four days after Russia's full-scale invasion of Ukraine, Turkey closed the straits to all warships, a move that principally affects Russia.