"Hundreds of foreign mercenaries in Ukraine have been destroyed by Russia's long-range precision weapons shortly after their arrival" to undergo training, the Russian defence ministry said in a statement.

"Most of the mercenaries have been destroyed in combat zones due to their low level of training and lack of real combat experience."

The Russian army said it has managed to stem the arrival of foreign mercenaries in Ukraine, estimating their current number in the pro-Western country at around 3,500.

Since the start of May, the arrival of foreign mercenaries "has virtually dried up," the defence ministry said, estimating that the total number "has nearly halved from 6,600 to 3,500 people."

On February 24, Russian President Vladimir Putin sent troops to Ukraine to "de-militarise" and "denazify" the pro-Western country.

A European official said in April that up to 20,000 mercenaries from the Russian private military company the Wagner Group, as well as from Syria and Libya, were fighting alongside Moscow's forces in Ukraine.