Shots have been fired around Donetsk international airport in eastern Ukraine with smoke billowing from the airport area, an eyewitness told Reuters.
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Detectives have charged 19-year-old Bilal Mumin with murder, grievous bodily harm and possession of an offensive weapon.
Members of the RMT on Arriva Rail North (Northern) walked out for 24 hours, with more stoppages due on Thursday and Saturday.
Police said a dozen shots were fired, but no arrests have been made and they are looking for a dark vehicle.