Russia on Thursday began huge joint military exercises with Belarus along the European Union's eastern flank in a show of strength that has rattled nervous NATO members.
Named Zapad-2017 (West-2017), the manoeuvres are scheduled to last until September 20. They are being conducted on the territory of Moscow's closest ally Belarus, in Russia's European exclave of Kaliningrad and in its frontier Pskov and Leningrad regions.
Moscow says the drills involve 12,700 troops, 70 aircraft, 250 tanks and 10 battleships testing their firepower against an imaginary foe close to borders with Poland and the Baltic States.
Russia's defence ministry insisted the manoeuvres were "of a strictly defensive nature and are not directed against any other state or group of countries."
But NATO claims Russia has kept it in the dark and could be massively underreporting the scale of the exercises, which some of the alliance's eastern members say involves more than 100,000 servicemen.
The war games come with tensions between Russia and NATO at their highest since the Cold War due to the Kremlin's meddling in Ukraine and the US-led alliance bolstering its forces in eastern Europe.
Moscow has dismissed fears over the drills -- the latest in a series of annual exercises that rotate around the vast country -- as fuelled by the "myth about the so-called 'Russian threat'".
-- 'Intention to threaten' --
But for NATO and its allies, especially jittery members such as Poland and the Baltic States which only broke free from Moscow's grip 25 years ago, such reassurances have not dampened suspicion.
"We have seen before that military exercises have been used as a disguise for aggressive actions against neighbours," NATO chief Jens Stoltenberg said in an interview with Russia's state-run RIA Novosti new agency released Thursday.
"We don't see an imminent threat against any NATO ally, but the best way for Russia to help to reduce tensions and to avoid or prevent misunderstandings, miscalculations, is to be transparent."
Lithuanian President Dalia Grybauskaite said her country could not ignore "the offensive nature of the Zapad exercise."
"Its scenario shows Russia's intention to threaten and to intimidate," she told AFP.
In Latvia, Foreign Minister Edgars Rinkevics said all relevant ministries were in a state of alert.
Poland meanwhile expressed concern that Russia could leave some of the equipment and troops in Belarus.
"Ukraine was attacked shortly after the Zapad 2013 exercises, and a few years earlier there was the attack on Georgia, also after large military manoeuvres," Poland Deputy Defence Minister Michal Dworczyk told the Polish PAP news agency.
President Vladimir Putin's spokesman defended Russia's right to hold exercises and rejected accusations the authorities had not been transparent.
"We do not accept reproaches," spokesman Dmitry Peskov told reporters on Thursday. He did not rule out Putin taking part in the drills.
Moscow has held a stream of exercises since ties with the West plunged in 2014 over Ukraine, with the military claiming some drills included nearly 100,000 troops.
Minsk has said the games will role play a conflict with a made-up rebel region backed by neighbouring European nations. Russia says they will simulate assaults by "extremist groups" trying to carry out "terrorist attacks".
Military expert Alexander Golts said Moscow "very skillfully manipulates the figures for such drills because it does not want to have to invite foreign observers".
"Russia at every drill is working on one and the same scenario -- how to deploy troops quickly," he told AFP.
The Kremlin has long blamed Washington for ratcheting up tensions by expanding NATO up to its borders and holding its own provocative drills.
The Russian war games come as Ukraine on Monday launched annual joint military exercises with the US and a host of other NATO countries.
Meanwhile non-aligned Sweden has mobilised 19,000 soldiers for its biggest drills in 20 years which also include units from across Scandinavia and the US.