NATO would not be able to rebuff a potential Russian attack on its eastern flank, according to an internal report cited on October 20 by German weekly Der Spiegel.
The paper, titled Progress Report On The Strengthened Deterrence And Defense Capability Of The Alliance, pointed to significant deficiencies.
"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 report as saying.
Even the strengthening of the NATO Response Force (NRF) has failed to ensure that it could "react rapidly and -- if necessary -- sustainably," it said.
The report cited a downsized command structure since the fall of communism as one of the paramount elements that has undermined the alliance's defense capabilities, Der Spiegel quoted the report as saying.
NATO spokeswoman Oana Lungescu declined to comment on the German magazine report but said that alliance "forces are more ready and able to deploy than at any time in decades."
Lungescu said that efforts are "under way to ensure that the NATO command structure remains robust, agile, and fit for purpose."
The alliance's command structure is to be discussed at a meeting of NATO defense ministers next month.
NATO's relations with Russia are at their lowest since the Cold War over the conflict in Ukraine.
After Russia annexed Crimea in 2014, NATO suspended its civilian and military cooperation with Moscow, as Ukraine announced its intention to seek membership in the alliance.