Russia's defence ministry says two of its navy destroyers forced away a Dutch submarine to stop it spying on an aircraft carrier in the Mediterranean. The sub was 20km (12 miles) from the Admiral Kuznetsov at the time of the incident. Russia had sent a flotilla to the Mediterranean ahead of an expected resumption of air strikes in Syria. NATO said it was monitoring the ships in a ‘measured and responsible way’: a spokesman for the Western military alliance did not go into details, but said it had been observing the fleet for some weeks. The Russian flotilla’s voyage through the English Channel and into the Mediterranean has rung alarm bells among NATO allies. Dutch military tweeted that they would give no comment on submarine operations. Dutch marine expert Jaime Karreman said that if true the incident was unprecedented. ‘It's pretty shocking that a submarine on a secret mission is discovered’, he told Dutch TV.