These images show the Russian submarine Rostov-on-Don travelling through the Strait of Istanbul and making its way to the Crimea ahead of an expected invasion of the Ukraine.

The Russian Navy vessel was photographed crossing the Strait of Istanbul, also known as the Bosporus, and entering the Black Sea on 13th February.

The submarine, reportedly carrying Novator Kalibr-PL cruise missiles and part of Russia’s Black Sea Fleet, has been operating in the Mediterranean Sea for 331 days following maintenance works in the Baltic.

While leaving Istanbul in Turkey, the Russian sub was accompanied by local Coast Guard vessels.

On 12th February, over 30 vessels of the Black Sea Fleet took to the sea to participate in exercises designed to defend the Crimean Peninsula, annexed by Russia from the Ukraine in 2014.

The naval war games focused on the protection of Black Sea Fleet bases and the regional economy from possible military threats.

Last week, UK Prime Minister Boris Johnson called the situation with the Ukraine, where around 100,000 Russian troops have been amassed around the border for some months, the “biggest security crisis that Europe has faced for decades”.

NATO has also boosted its forces in the region amid fears that President Putin plans to invade the Ukraine at any moment.

Britain’s Parliamentary Under-Secretary of State for the Armed Forces James Heappey said he feared a Russian attack was “very imminent” on Monday and urged Brits to evacuate the Ukraine.

The Kremlin has claimed that it has no plans to invade the Ukraine, but wants the West to keep the country and other former Soviet nations out of NATO.