Russian officials have accused Ukraine of launching a drone attack on a building in Moscow, causing an explosion that was heard across the city's business district.
Mayor Sergei Sobyanin said air defences had shot down the drone with its debris falling on the city's Expo Center.
Unverified footage on social media appeared to show thick grey smoke rising into the night sky over Moscow.
One Russian state-owned news agency, Tass, reported that one of the outer walls of the centre had partially collapsed, citing emergency services.
Until earlier this year, Moscow remained untouched by the war in Ukraine, but in recent months has been targeted by drone strikes.
Ukrainian President Volodymyr Zelensky said at the time that the war was "returning to the territory of Russia" and that this was an "inevitable, natural and absolutely fair process".
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