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Explosions were heard in the centre of the Ukrainian capital Kyiv early on Wednesday, the city's mayor says.
Vitali Klitschko said blasts rocked the central Shevchenkivskyi district and emergency services had been dispatched.
Air defence systems are at work, Kyiv governor Oleksiy Kuleba says.
BBC reporters heard loud explosions shortly after the air raid siren sounded. Russia has repeatedly targeted Ukrainian energy infrastructure since October with missiles and drones.