Tensions between Moscow and Kiev reached boiling point earlier this year after Russia massed more troops near the contested borders. Since 2014, at least 14,000 people have been killed in the conflict in eastern Ukraine.
Now, Ukrainian President Volodymyr Zelenskiy warned an all-out war with Russia could be a “possibility”.
Speaking at the Yalta European Strategy (YES) summit, Mr Zelenskiy said: “I think there can be.
“It’s the worst thing that could happen, but unfortunately there is that possibility.”
Mr Zelenskiy also revealed he has attempted to meet with Russian President Putin to discuss the conflict but no meeting has yet happened.
He continued: “Honestly, I don’t have time to think about him.
“I’m more interested in whether we can really meet substantively, not declaratively as he does with some states.
“It seems to me that today… they do not see the sense in resolving issues.
“End the war and resolve conflict issues quickly – they don’t want this.”
The drills will involve live fire but have sparked alarm as Belarus is part of quasi buffer zone between Europe and Russia.
In August last year, huge demonstrations broke out in Belarus following a disputed election which gave Alexander Lukashenko a sixth term as President.
Russia backed Belarus and said they would be willing to send troops into the country if required.
Police have cracked down on protesters and several prominent opposition figures have been arrested or imprisoned.
Moscow has been a vital ally for Belarus after the West imposed sanctions on Minsk following the crackdown.
Mathieu Boulegue, a research fellow at the Chatham House think tank, said: “Lukashenko has gone from not really being willing to participate [in the drills] back in 2017 to being one of the most boastful, in a way, about how important this exercise is in terms of the intimidation that it represents against the West.”
The two Presidents spoke for nearly four hours and announced 28 programs strengthening integration were approved.
These programs fall under a 1999 union agreement that calls for close political, economic and military ties.
However, it does stop short of a full merger and includes establishing a single gas market by the end of 2023.
Despite Russia backing Belarus, their relationship has been strained after Mr Lukashenko scolded Moscow for trying to force him to relinquish control of economic assets.