Russia and Belarus began war games on NATO's eastern border on Friday, with Europe on high alert after Poland accused Moscow of flying drones in its airspace.
Poland, Lithuania and Latvia have ramped up security ahead of the Zapad 2025 drills, with Poland ordering the complete closure of its border with Belarus for their duration.
'The joint strategic manouevres of the Russian and Belarusian armies ... have started,' Russia's defence ministry said in a statement.
The organisers say their 'defensive' drills will not exceed 13,000 personnel.
But European allies fear Zapad could be used to rehearse an invasion of Europe, after 2021's drills saw a huge build up of forces used to attack Ukraine months later.
