Moscow's only aircraft-carrier takes part in the largest Russian warship deployment since the Cold War as European naval forces track its route through the English Channel.
Russia has deployed several warships on an eyebrow-raising voyage along western Europe towards Syria.
The ships are due to cross the English Channel before entering the Mediterranean through the Strait of Gibraltar. European naval forces, already on the edge due to strained ties with Russia over the war in Syria, have been watching the fleet closely since they set sail from the Barents Sea on Saturday.
Norway on Wednesday released pictures taken by surveillance aircraft of the fleet sailing in international waters towards Scotland.
Speaking to Reuters on condition of anonymity, a NATO diplomat said that all of Russia's Northern Fleet and most of its Baltic Fleet were included "in the largest surface deployment since the end of the Cold War."
According to Russian media, the fleet includes Russia's only aircraft-carrier, the Admiral Kuznetsov, which is carrying fighter jet, and the Soviet-era nuclear-powered battle cruiser Pyotr Velikiy, or Peter the Great. Anti-submarine warships and support ships are also included.
It is unclear why Russia is sending its only aircraft-carrier to the eastern Mediterranean to take part in operations in support of Bashar al Assad's regime in Syria, considering that Russia already has access to airbases in regime-controlled territories.
The Admiral Kuznetsov ship is relatively small and has been dismissed by experts as a "piece of junk" that is likely to get damaged on the long, expensive voyage.
Dmitry Gorenburg, a senior research scientist at Harvard's Davis Center for Russian and Eurasian Studies, told the Washington Examiner that the aircraft-carrier "pretty much always goes out with a tugboat."
"On several of its most recent voyages, it's had to put into port to have its boiler worked on," he said.
But international relations analyst Peter Apps said Moscow's intention behind the deployment was "to show that it can emulate Washington by sending a task force thousands of miles and then conducting weeks or months of military activity – an exercise that will highlight Russia's renewed military capability."
"On previous passages through the North Sea, the carrier has deliberately operated jets and aircraft close by Norwegian oil platforms, an act of intimidation that forced nearby civilian helicopters to be grounded," Apps pointed out. "This time, there are reports the carrier may conduct bombing exercises in international waters north of Scotland."
UK, Belgium and the Netherlands on guard
Britain on Thursday said it would keep a close eye on the fleet. "When these ships near our waters we will man-mark them every step of the way," British Defence Minister Michael Fallon said. "We will be watching as part of our steadfast commitment to keep Britain safe."
Dutch and Belgian ships will also be keeping watch, Dutch Royal Navy Commander Rob Verkerk said in a tweet.
ZrMs Evertsen stand-by om Kuznetsov-groep eventueel te escorteren in geval van passage door Noordzee. pic.twitter.com/gNa21wXPU5— Rob Verkerk (@GeneraalVerkerk) October 19, 2016
Although the monitoring of Russian warships in international waters is a regular activity for NATO and its allied nations, the passage of the large fleet comes as relations between Russia and the West reach new lows, particularly over disagreements on the wars in Syria and Ukraine.
Recent efforts to bring about a lasting ceasefire in Syria between the Russian-backed regime and Western-backed opposition forces have proven futile. Each side has blamed the other for the failure.
A breakdown in communication between Russia and the US since the truce fell through have increased tensions to levels not seen since the end of the Cold War, with some analysts speculating that disagreements on Syria could even spark World War III.