WARSAW (Reuters) - Russia could be ready militarily to attack NATO countries in five to eight years' time if it chose to do so, Germany's top military official said, once it has rebuilt its forces hit by the impact of the Ukraine war.

       "By then, based on our analysis, Russia (will have) reconstituted its own forces to a degree that an attack against NATO soil could be possible," Lieutenant General Carsten Breuer told reporters during a visit to Poland.

       "I am not saying it will take place but that it could be possible," he said late on Wednesday.

       Russia's invasion of Ukraine in February 2022 has triggered the deepest crisis in Moscow's relations with the West since the 1962 Cuban Missile Crisis.

       But Moscow has regularly dismissed Western suggestions that it might consider an attack on NATO as complete nonsense. President Vladimir Putin reiterated last month that Russia had no designs on any NATO country, though he said it would shoot down any F-16 fighters supplied by the West to Ukraine.

       Of NATO's 32 members, six European nations share a border with Russia: Norway, Finland, Estonia, Latvia, Lithuania and Poland.

       Russia now appears increasingly in the ascendancy in Ukraine, where the conflict is characterised by both attritional trench combat reminiscent of World War One and high-tech drone warfare.

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       Moscow now controls almost a fifth of Ukrainian territory including the Crimea peninsula it annexed in 2014.

       "We see that Russia is producing a lot of war-fighting material and it is not putting all of this material to the frontline in Ukraine... so in 2029 we have to be ready," Breuer, Germany's chief of defence, said.

       "What we see is a threat in five to eight years."

       Ukrainian officials have said their armed forces number around 800,000, while in December Putin ordered Russia's forces to be increased by 170,000 troops to 1.3 million.

       Beyond personnel, Moscow's defence spending dwarfs that of Ukraine. In 2024 it earmarked $109 billion for the sector, more than twice Ukraine's equivalent target of $43.8 billion.

       (Reporting by Justyna Pawlak; Editing by Gareth Jones)