Some 90,000 troops will take part in the NATO military alliance's Steadfast Defender 24 exercise, the biggest since the 1988 Reforger drill during the Cold War.

"Of course it is a threat to us, that is how we treat it, and we are constantly taking appropriate measures to deal with it," Kremlin spokesman Dmitry Peskov said.

"The alliance has been moving its military infrastructure towards our borders for several decades without ceasing," he told reporters when asked about the drills.

The exercises, which began last week, are designed to simulate NATO's response to an attack from a rival like Russia, and will involve some 50 naval vessels.

They will be composed of a series of smaller individual drills and will span from North America to NATO's eastern flank, close to the Russian border.