Explosions rang out, artillery shells screeched and jets roared as a few dozen men ¡ª including U.S. military officials ¡ª watched through binoculars as Belarusian and Russian troops charged across a training ground.

Moscow and key ally Minsk say the drills, called Zapad, are designed to simulate a possible invasion of their territory.

But it is NATO¡¯s eastern flank that has its tail up about a possible attack ¡ª spooked by the movement of thousands of troops just days after Russian drones were downed over Poland and with Warsaw warning ¡°open conflict¡± is closer than at any point since World War II.