Russia on Tuesday dismissed Western concerns over its military exercises with Belarus next month, calling them "purely defensive" and not directed against any specific enemy.

"The Zapad-2017 exercises have an anti-terrorism focus as well as a purely defensive character," Deputy Defence Minister Alexander Fomin said at a press briefing.

He slammed international media for "disseminating myths about the so-called 'Russian threat'" in coverage of the drills set to be held along NATO's eastern flank from 14 to 20 September.

"Some even say that the Zapad 2017 exercises are a launching point for 'invasion or 'occupation' of Lithuania, Poland, or Ukraine," Fomin added.

NATO Secretary General Jens Stoltenberg in July said that he had "every reason to believe" the drills will have "substantially more troops participating than the officially reported numbers."

On Friday, Stoltenberg urged the Kremlin to ensure transparency and predictability during the exercises, warning that NATO "would be watching very closely."

The exercises in western Russia, Belarus and the western Russian exclave of Kaliningrad have deeply worried neighbouring NATO allies, with Lithuania claiming that as many as 100,000 troops could attend.

Fomin said that "about 12,700" troops will be participating in the exercises, including 7,200 from Belarus and 5,500 from Russia. About 3,000 will be in Belarus during the exercises, he said.

"Despite the fact that the main part (of the drills) are to be held on Belarusian territory, the scenario assumes an artificial enemy, which has nothing to do with any specific region," he added.

Belarus' military chief of staff Oleg Belokonev indicated, however, that the exercises' scenario does involve an assumed threat from neighbours to the west.

"The scenario says that there is a coalition of interested states in the west -- Weisbaria, Weistoria and Lubinia -- on the scenario map they are located where Poland, Lithuania and Latvia are," he said at a briefing on Tuesday.

Belokonev added that Minsk fears the West seeks "to destabilise the situation in the country" and that "this scenario is how all recent armed conflicts have started."

He also gave a higher figure for the number of troops participating, saying it will be "13,800 servicemen."

In the two-stage event, the armed forces of Russia and Belarus will first "isolate areas where illegal armed groups and the enemy's sabotage-reconnaissance groups are active," Fomin said.

In the second stage they will practise "military action while repelling aggression against the union state (Russia and Belarus)."

The war games' scenario is that "extremist groups" have infiltrated Russia and Belarus and are planning "acts of terrorism" while receiving "outside support" from the air and sea, Fomin said.

"We believe that the situation in the drills' scenario could come up in any part of the world," Fomin said.