Three Baltic NATO states on Friday questioned the purpose of major war games by Russia and Belarus close to their borders, accusing their Soviet-era master Moscow of a secret "anti-West" agenda.
Lithuania, Latvia and Estonia, former Soviet states that are now members of the western alliance, all expressed concern about the scale of military manoeuvres publicly intended to prepare defences against terrorism.
"Russia has officially stated that these are anti-terrorism exercises. But the number of participants and amount of military equipment indicates that that this is not their agenda", Lithuania's Defence Minister Juozas Olekas told AFP.
"Every country has the right to conduct exercises, but we are concerned that these exercises are not transparent," he added.
The manoeuvres involve around 13,000 servicemen and hundreds of weapons systems including warplanes, artillery and armoured vehicles, a Belarus defence ministry spokesman told the Russian Interfax news agency on Friday.
"The Kremlin claims that the exercise is about fighting terrorism, but based on the information we have on Zapad 2013, the exercise has an anti-West agenda," Estonia's Deputy Chief of Staff, Lieutenant Colonel Eero Rebo, told AFP on Friday.
Launched Friday, the manoeuvres are being held in Belarus and the Kaliningrad exclave, which is sandwiched between NATO members Lithuania and Poland.
They will end next Thursday.
Lithuania, Latvia and Estonia, which joined NATO and the EU in 2004, have repeatedly said they were concerned by a Russian military build-up near their borders.
"If you look at the Baltic sea region, the strategic balance has been changing quite drastically in the last decade, and not in our favour," Latvian Defence Minister Artis Pabriks told AFP on Friday.
"We are concerned because we see such large-scale exercises in context", he added.
In 2010, NATO approved special defence plans for Lithuania, Latvia and Estonia, which have a combined population of just over six million.
Later this year the NATO alliance will hold its major Steadfast Jazz exercise in the Baltic region and Poland, with around 6,000 North Atlantic Treaty Organisation troops.
The three Baltic states had all been under the yolk of Soviet rule for decades after World War II until until 1991.