A Ukrainian drone struck a storage tank at Russia's Moscow Oil Refinery on Thursday morning. The refinery, in Moscow's Kapotnya district, is one of the city's most important fuel-processing facilities. In the videos posted to social media, the blast occurred at the fuel storage tank, sending its roof flying into the air and triggering a massive fire. Flames and black smoke were then seen rising from the refinery. Russian officials called it one of the biggest attacks by Ukraine on Moscow - but what really happened?