Ukraine's military has said it struck an oil refinery in Russia's Saratov region in an overnight drone attack, causing explosions and destruction, according to an army statement, as daily aerial exchanges intensify with diplomatic momentum to end the war in play. Saratov's governor said on Sunday that one person was killed and several residential apartments and an industrial facility were damaged, but did not mention the oil refinery being struck. "[Ukrainian] drones are targeting … deeper into Russian territory [than] in the past, where previous attacks have been focused on the line of contact in the south and the western parts of Russia," said Al Jazeera's Osama Bin Javaid, reporting from Moscow. It is still unclear whether Ukraine's claims that it hit a refinery are true, he added. Ukraine's military also said on Sunday that it had taken back a village in the Sumy region from the Russian army, which has made significant recent gains there.

People were filmed fleeing a fire at a Russian oil refinery in Ryazan, about 200 kilometres southeast of Moscow, after a Ukrainian drone attack. The facility accounted for almost 5% of the country's oil refining output last year.

Andriy Kovalenko, head of Ukraine's centre for countering disinformation, said on Telegram that an oil refinery in Ryazan had been hit, as well as the Kremniy factory in Bryansk that Kyiv says produces missile components and other weapons. Bloggers on Telegram posted images and videos of fires raging at the Ryazan facility, which covers around 6sq km (2.3sq miles). Verified footage shows people fleeing from the site in cars and on foot as a fireball rises into the sky. BBC Verify used video footage to establish the location of two fires at the refinery. One video shows a fire near the northern entrance, whose location was matched by the road layout, signs and fences.

Fox News Flash top headlines are here. Check out what's clicking on Foxnews.com. Fire broke out at an oil refinery in northwestern Russia on Sunday, resulting in deaths and injuries, local officials said. The regional governor said the fire was not caused by a Ukrainian drone strike and investigators opened a criminal case on suspicion of negligence. The fire near the city of Ukhta in Russia's northwestern Komi Republic left at least three people injured, Komi's emergencies ministry said.

New drone footage obtained by The Associated Press news agency showed how months of relentless Russian artillery pounding has devastated Chasiv Yar. The town was once home to 12,000 people, but the footage reveals it is now almost deserted and barely a building remains intact. The United States accused Russia of breaking the international ban on chemical weapons by using the choking agent chloropicrin against Ukrainian troops. Chloropicrin is listed as a banned agent by the Hague-based Organisation for the Prohibition of Chemical Weapons (OPCW). The US said Moscow was also deploying riot control agents "as a method of warfare" in Ukraine.