A convoy of Russian warships heading for the Mediterranean has sailed down the English Channel - "marked every inch of the way" by the Royal Navy.
Video footage showed the Russian task force, including the aircraft carrier Admiral Kuznetsov, off the coast of Dover.
The fleet also reportedly includes the Pyotr Velikiy battlecruiser, the Severomorsk anti-submarine ship, the Vice-Admiral Kulakov destroyer and other support vessels.
The most sensitive part of the fleet's journey was through the English Channel's narrowest point at the Strait of Dover.
Vladimir Putin's armed flotilla is believed to be heading to Syria to support Russia's military operations in the war-torn country.
Asked whether the Russian deployment was an indication that Moscow regarded Britain as weak, a Downing Street spokesman said: "I would reject suggestions that the Russians feel we are too weak. Clearly, we are not weak at all."
A Ministry of Defence spokesman said: "It is pretty unambiguous that they have set a course to pass through the Dover Strait."
He added: "When they are clear of the Dover traffic separation scheme, they will probably break back out in a formation scheme and be on their way.
"We still don't know where that is and how they are going to get there, but everything so far has been exactly how we would have expected."
British ships, including two destroyers - HMS Duncan and HMS Dragon - were deployed earlier this week and have been monitoring the Russian vessels.
The Russian fleet, which has been heading south from the Norwegian Sea, has also been escorted by frigates HMS Richmond and HMS Duncan.
Defence Secretary Sir Michael Fallon said the Russian naval deployment was aimed at "testing" British capabilities.
"The Russian fleet that is now sailing from the north, presumably down into the Mediterranean, is clearly designed to test the alliance.
"It's being marked every step of the way by the Royal Navy and ships and planes of other NATO members as well.
"It's clearly designed ... to test our response, and any weaknesses in the alliance, and we must make sure we respond in due measure.
"That fleet will be marked, shadowed every inch of the way."
Shadowing ships is a regular task for the Royal Navy, which has been supported by Royal Air Force surveillance aircraft this time, it is understood.
Images of the Russian convoy, taken from a North Sea oil rig, also show the fleet being shadowed by a NATO Hercules C-130.
It is feared the powerful force could soon join in attacks on Syria's besieged city of Aleppo .
A NATO official said: "Russia has the right to operate in international waters. There are plans in place for NATO navies to monitor the Russian ships as they head for the Mediterranean.
"At the same time, the deployment of the carrier group to the eastern Mediterranean does not inspire confidence that Russia is working towards a political solution to the conflict in Syria."
According to the Russian news agency Tass, Russia's Defence Minister Sergei Shoigu told a meeting in September the plan was to bolster the "combat capabilities" of the country's Mediterranean fleet.
A statement from the fleet to the agency said: "Special focus will be made on safeguarding security of maritime traffic and other types of maritime economic activity of Russia and also on responding to the new kinds of modern threats such as piracy and international terrorism."