By Robin Emmott
BRUSSELS (Reuters) - Russia sought to reassure NATO on Thursday that its war games in September would respect international limits on size, but NATO's chief remained wary about their scale and scope.
Russia and Belarus aim to hold maneuvers that some NATO allies believe could number more than 100,000 troops and involve nuclear weapons training, the biggest such exercise since 2013.
NATO allies are nervous because previous large-scale Russian exercises employed special forces training, longer-range missiles and unmanned aerial vehicles.
Such tactics were later used in Russia's annexation of Crimea in 2014, its support for separatists in eastern Ukraine and in its intervention in Syria, NATO diplomats say.
After a meeting on Monday of the NATO-Russia Council, a liaison forum, Moscow's ambassador to the North Atlantic Treaty Organization called on the alliance to stop "demonising" the exercises.
"Today was a major step, we were asked to brief on (the) Zapad exercises and I really hope this will help stop the demonising ... and rumors about threats," Alexander Grushko told reporters, using the Russian name of the maneuvers.
"The problem is..., we read a lot of speculation and have heard from NATO countries. Some were saying it would be 200,000 in number, some were saying 100,000. Today we gave our figures," Grushko told a news conference. He declined to give details.
Under a Cold War-era treaty known as the Vienna document, which sets out rules for large-scale exercises, war games should not number more than 13,000 troops, should be publicized well in advance and should be open to observers.
Grushko said that if Zapad reached the Vienna threshold, Moscow would invite observers.
NATO Secretary-General Jens Stoltenberg declined to discuss Russian troop numbers that were divulged at the session of the NATO-Russia Council, which brings together NATO envoys and Russia's top diplomat to the alliance.
However, he said that judging by past experiences, Moscow could still mask the true size and scope of the war games.
"From previous experience, related to previous exercises, we have every reason to believe that there may be substantially more troops participating than the official reported numbers," Stoltenberg told a separate news conference.
The Baltic states have said they will press the United States and NATO to take additional security measures in the region. Estonia has said Russia may leave troops in Belarus after the exercises finish.
Such a move could see Russian troops on the border with Poland, Lithuania and Latvia just as U.S.-led NATO stations multinational battalions in the Baltic region in response to Russia's 2014 annexation of Ukraine's Crimea.
Despite what officials said was a calm and professional meeting of the NATO-Russia Council, the public comments pointed to tensions that persist between Russia and NATO since Crimea's annexation and Moscow's support for separatists in Ukraine.
Little progress appeared to be made on efforts to fly warplanes more safely over the Baltic Sea after the latest intercepts that both sides say involved dangerous pilot maneuvers. NATO wants Moscow to file the flight plans of Russian pilots, respond to air traffic control or identify themselves with cockpit transmitters, known as transponders.
The Kremlin says all Russian flights over the Baltic are conducted in strict accordance with international law.
(Additional reporting by Philip Blenkinsop; editing by Mark Heinrich)