Diplomats from three countries part of NATO's eastern flank have raised alarm bells and urged Western Europe not to undermine Russia.

       Estonia, Lithuania and Latvia echoed warnings already being issued by other countries about the Kremlin's increasing aggressiveness.

       While Russia is still fighting Ukrainian troops two years into the unlawful invasion of the eastern European country, officials from the Baltic states noted Russia has the capacity to "pivot quickly" and launch an attack against them.

       In a joint article penned for The Sunday Telegraph to mark the 20th anniversary of the Baltic countries' accession to NATO, the Estonian ambassador Viljar Lubi, the Latvian ambassador Ivita Burmistre, and Lithuania’s charge d’affaire Lina Zigmantaite, wrote: "We are acutely aware that Russia’s war economy and battle-hardened military can pivot quickly from south to west.

       "We agree with intelligence assessments that a sharp strategic challenge to our defence and deterrence could come in as little as three years or even less.

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       "We on the east side of the Baltic Sea have few natural frontiers, and nowhere to retreat to."

       The diplomats added the three nations are already facing daily "hybrid attacks" including cyber warfare, which aims at spreading disinformation and distracting the population.

       In the face of a similar threat, the three countries and their allies should remain "ready to respond quickly" to any potentially devastating challenge arising.

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       This comes just days after a brazen Vladimir Putin dismissed Western fears Russia is planning an attack against a NATO member state as "drivel".

       He said: "The idea that we will attack some other country - Poland, the Baltic States, and the Czechs are also being scared - is complete nonsense. It's just drivel."

       Yet, he sparked concern by warning the delivery of F-16 fighter jets to Ukraine, promised by a number of European countries, could spell trouble for the West.

       He said: "Of course, if they are used from the airfields of third countries, they become a legitimate target for us, wherever they are."

       The diplomats' warning also came after the top military chief of Estonia said his country should double its defence spending over the next two years to be ready not just to defend itself against a possible Russian invasion but also to deal a "decisive" defeat.

       General Martin Herem, the commander of the Defence Forces in Estonia, said: If you show your face over my border, the decisive victory must come very quickly: not by months and years, but days and weeks.

       "If we really believe that it may come in three years, then we have to make decisions today."

       An attack on Estonia or any other NATO member state would risk dragging the whole of the Western military alliance into a conflict against Russia, due to its collective defence principle.