Jens Stoltenberg said Russia must accept NATO observers under guidelines agreed between the two powers for exercises of more than 30,000 troops, according to Peeblesshire News citing the NATO chief's BBC interview.

He dismissed Moscow’s claims that the Zapad 2017 exercise with Belarus would feature less than 30,000 troops, claiming Russia was “under-reporting” and “using loopholes” to avoid scrutiny, with around 100,000 estimated to be taking part.

Mr Stoltenberg also warned that exercises in the past have been used as a way to build up to invasions of other territories.

Read alsoUK defense chief says Zapad 2017 drills aimed at provoking NATO“That happened in Georgia in 2008 when they invaded Georgia and it happened in Crimea in 2014 when they illegally annexed Crimea.

“So we call (on) Russia to be fully transparent.”

The exercise will run from September 14 to 20 not far from the borders of NATO allies Estonia, Latvia, Lithuania and Poland.

Read alsoPresident: Zapad 2017 drills pose possible threats for UkraineBritain has a battle group in Estonia, while NATO has stationed troops in the other Baltic states and Poland.