Little is known about the shadowy paramilitary group which is believed to be linked to Russian oligarch Yevgeny Prigozhin, who is himself an associate of President Vladimir Putin.
Mozart - which was set up after the war started by an ex-US commander and is funded by donations - provides military training, but Mr Bain says what they teach is really"a lot of common sense." In a field in the Donetsk region, Mozart's foreign instructors take a group of around twenty Ukrainian soldiers through their paces.
"That kind of training is very useful because even with combat experience, we can always learn new stuff," he says.
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