NATO reportedly has moved to expel dozens of suspected Russian spies from its headquarters in Brussels in the latest sign of a renewal of tensions between the western military alliance and Moscow. 

The Guardian reported that NATO decided last month to mandate that all non-member state delegations reduce their staff to no more than 30 people. The new rule only affected Russia, though estimates of the exact number of Russian delegates vary. The Kremlin says it has only 37 people accredited to work in Brussels. However, a diplomat from a NATO member state told The Guardian that in fact 61 people were part of the delegation. Other NATO sources told the paper the number was as high as 90. 

Regardless of the number, the paper reported that NATO diplomats estimate that approximately half of the Russian contingent was working on behalf of Moscow's intelligence service. In practice, the paper reported, only Russia's ambassador to NATO, his deputy, his secretary, and his driver, were allowed to traverse the alliance's offices without being escorted.

NATO Secretary General Jens Stoltenberg denied in an interview that the new rule specifically targeted Russia, saying, "With the Russians we have decided to suspend all practical co-operation but to maintain the channels of political and military dialogue and contact. A delegation of 30 is more than enough to do that."

The Guardian also reported Sunday that NATO has revived the Cold War-era practice of using hotlines to the Kremlin and the Russian general staff in an effort to reduce the chances of military confrontation. Stoltenberg disclosed that NATO jets had intercepted an increasing number of Russian planes in recent months over the Black, Baltic, and Norwegian seas.

"It’s important to have contacts military to military in a normal situation so that if something not normal happens, you’re able to clarify misunderstandings, to avoid situations out of control," Stoltenberg told The Guardian.

NATO foreign ministers, including U.S. Secretary of State John Kerry, were due to gather for a meeting Wednesday in Antalya, Turkey. The meeting would come one day after Kerry planned to meet with Russian President Vladimir Putin and Foreign Minister Sergey Lavrov in the Black Sea resort of Sochi. 

However, while the State Department said Monday that Kerry would meet Putin and Lavrov, the Kremlin said Putin's attendance had yet to be confirmed. The Russian Foreign Ministry also blamed the U.S. for the ongoing civil war in Ukraine. 

"The Obama administration chose the path of scaling back bilateral relations, proclaimed a course of isolating Russia on the international arena and demanded that those states that traditionally follow the lead of Washington support its confrontational steps," it said in a statement.

Western nations say Russia supports the separatists with arms and manpower, and even directs some battlefield operations — all claims Moscow denies. In return, the Russians bristle at Washington's provisions to Ukraine of military assistance in the form of hardware and training.

In late April, troops from the United States and Ukraine kicked off joint training exercises intended to help bolster Ukraine's defenses. The exercises, dubbed "Fearless Guardian-2015," sparked outrage from Russia, which described them as a potential cause of destabilization.

The Associated Press contributed to this report. 

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