(Reuters) -Belarus protested to Ukraine’s ambassador on Thursday after saying it had downed a Ukrainian S-300 air defence missile in a field, during one of Russia’s heaviest aerial onslaughts against Ukraine since the start of the war in February. The military commissar of the Brest region, Oleg Konovalov, played the incident down in a video posted on social media by the state-run BelTA news agency, saying locals had “absolutely nothing to worry about. Unfortunately, these things happen”. He compared the incident to one in November, when an S-300 believed to have strayed after being fired by U…