The British navy said Thursday it tracked a Russian submarine navigating through the English Channel for three days, as it steps up efforts to police its seas against such threats.

A British naval supply ship with an on-board helicopter was deployed to track the stealthy Kilo-class submarine Krasnodar and the tug Altay, the Royal Navy said in a statement.

The Russian ships had arrived from the North Sea and entered the Channel.

"Expert aircrew were prepared to pivot to anti-submarine operations if Krasnodar had dived below the surface," the statement said.

But it sailed on the surface throughout the operation, despite unfavorable weather conditions.

"There is nothing like a Russian submarine to focus the mind for any mariner," Royal Navy Captain James Allen said in a statement.

Near the island of Ouessant, off northwest France, the British said they handed over monitoring of the vessels to a NATO ally, without saying which one.

Defense Secretary John Healey announced on Monday the launch of a multi-million dollar program to improve the Royal Navy's capabilities in the face of Moscow's "underwater threats."

Healey said a Russian spy ship last month pointed lasers at Royal Air Force pilots tracking its activity near U.K. waters, BBC News reported. The U.K. said the ship was being used for gathering intelligence and mapping undersea cables.

Meanwhile, NATO Secretary-General Mark Rutte on Thursday issued an ominous warning to his European audience at a speech in Berlin, declaring: "We are Russia's next target." Rutte said Europe must prepare for a confrontation with Russia on the kind of scale "our grandparents and great-grandparents endured."

Separately, Britian's armed forces minister, Al Carns, warned: "The shadow of war is knocking on Europe's door once more. That's the reality. We've got to be prepared to deter it."

Increased Russian submarine activity off U.K.

According to London, Russian submarine activity in British waters has increased by about a third over the past two years.

Earlier this month, the U.K. and Norway signed a cooperation agreement to jointly operate a fleet of frigates to "hunt down" these submarines in the North Atlantic.

The British military carried out a similar shadowing operation in July, after spotting the Russian sub Novorossiysk in its territorial waters.

In January, Secretary Healey told Parliament the Royal Navy was tracking a Russian spy ship called the Yantar that passed through U.K. waters, warning Russia's President Vladimir Putin: "We know what you're doing."

The Royal Navy also revealed that in late December the frigate HMS Somerset had tracked a Russian naval group as it sailed from the North Sea to the English Channel, although the group had stayed in international waters.

In November 2024, British jets were scrambled to monitor a Russian reconnaissance aircraft flying close to U.K. airspace, just days after NATO jets were mobilized when Russian aircraft were spotted over the Baltic Sea and off the coast of Norway.

In September last year, Royal Navy warships spent a week "closely shadowing" four Russian vessels in U.K. waters, while two Royal Air Force jets scrambled to intercept two Russian aircraft operating near the U.K., the navy said.