NATO would be unable to repel a Russian attack on its Eastern European members, according to an internal alliance document cited by the German magazine Der Spiegel (German language) in its Saturday edition.

The internal document, titled "Progress Report on the Strengthened Deterrence and Defense Capability of the Alliance," questioned the ability of the NATO Response Force to "react rapidly and – if necessary – sustainably."

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"NATO's ability to logistically support rapid reinforcement in the strongly expanded territory of the European commander's area of responsibility has atrophied since the end of the Cold War," Der Spiegel quoted the document as saying.

It attributed NATO's deficiencies to a smaller command structure since the end of the Cold War and logistical difficulties on the alliance's eastern flank.

NATO's relations with Russia have soured over Moscow's intervention in Ukraine.

Poland as well as Scandinavian and Baltic member states feel threatened by Russia and have urged the alliance to bolster its eastern flank against possible aggression.

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In response, NATO has sped up the deployment and increased the size of the Response Force to 40,000 troops.

In 2014, NATO members decided to create a Very High Readiness Joint Task Force consisting of four battalions to act as a spearhead and deterrence against a possible Russian attack.

cw/aw (AFP, dpa)