New Delhi, May 22 -- Ukrainian drones smashed into another Russian refinery overnight, starting a fire that produced huge clouds of black smoke, President Volodymyr Zelenskyy said Thursday, in what appeared to be the latest long-range attack on Moscow's vital oil industry.

The drones targeted the Syzran oil refinery more than 800 kilometers (500 miles) inside Russia, Zelenskyy said on social media, where he posted a video of the aftermath.

It was impossible to verify the video or independently confirm the attack. The governor of Russia's Samara region, Vyacheslav Fedorishchev, said two people were killed by Ukrainian drones in Syzran, but he did not mention the refinery. Russia's Astra news outlet said Ukrainian drones struck the Syzran...