Editor's note: The article was updated after sources in Ukraine's military intelligence agency (HUR) confirmed the attacks in a comment for the Kyiv Independent.
Drones operated by Ukraine's military intelligence agency (HUR) attacked the Ryazan Oil Refinery and a refinery in Voronezh Oblast overnight on May 1, military intelligence sources confirmed for the Kyiv Independent.
Russian authorities reported on drone strikes against the two oblasts earlier on May 1, with claims being spread on the Russian Telegram channels that the Ryazan refinery was on fire.
Ukrainian media outlets subsequently reported that Ukraine's military intelligence agency was behind the attacks.
The first four explosions could be heard at the Ryazan refinery at around 2 a.m. local time, after which a large fire started on the facility's territory, the sources said.
The Voronezh Oblast refinery was also hit, the sources confirmed, without elaborating on the consequences.
According to Russian media, fragments of a downed drone also damaged buildings in Voronezh Oblast.
The Russian Defense Ministry claimed its forces downed six Ukrainian drones overnight: three over Voronezh Oblast, one over Ryazan Oblast, one over Belgorod Oblast, and one over Kursk Oblast.
Ukrainian forces have recently launched a series of drone strikes aimed at damaging Russia's oil industry. Attacks against oil depots in Russia's Smolensk Oblast last week destroyed 26,000 cubic meters of fuel, security sources told the Kyiv Independent.
The Ryazan Oil Refinery, the largest plant operated by the Rosneft company, was reportedly targeted also back on March 13.
The strikes against Russia's oil industry have prompted criticism from U.S. officials, who have made it clear that Washington does not support Ukraine's targeting of oil refineries, citing fears that it could threaten the global energy market.
Ukraine retorted that it considers Russian refineries to be legitimate military targets.
Igor Kossov
