A Russian attack helicopter mistakenly fired at least one rocket into a crowd of spectators during a large-scale military exercise in western Belarus simulating a counterattack against NATO forces.

The Russian military acknowledged that a rocket was fired by accident by a helicopter, but insisted that no one was hurt in the incident. It also would not say when or where the incident took place.

However, several Russian online media portals have reported that as many as three people were injured and two vehicles were destroyed.

A video posted on the British news site theguardian.com showed two helicopters flying low over a field where several men dressed in camouflage were watching the drills. One of the helicopters fired several rockets that appeared to hit a vehicle close to the spectators.

The helicopter drill was part of Zapad, a large-scale joint military exercise with Belarus taking place along the border with NATO countries west of Russia.

The exercises, which began Thursday and run through Wednesday, have raised concerns in the Baltic nations that Russia may be using the drills to prepare for a possible future invasion — in the same manner as Moscow prepared for its annexation of Crimea from Ukraine.