Kyiv said Monday its forces had recaptured an oil and gas drilling platform in the Black Sea that had been controlled by Moscow since 2015.
The platform is roughly halfway between the Moscow-annexed Crimean peninsula and the coast of Ukraine's southwestern Odesa region.
"Ukraine regains control of the so-called Boyka Towers (platform)," Kyiv's military intelligence said in a statement.
It said it had established control of drilling platforms and rigs in what it called a "unique operation."
"During one phase of the operation, a battle took place between Ukrainian special forces on boats and a Russian Su-30 fighter jet," it said, claiming that Moscow's plane was "hit and forced to retreat."
It released a video of boats circulating around the oil and gas platform, before its troops are seen firing into the air.
Russia annexed Crimea and much of the surrounding waters in 2014, and has accused Ukraine of trying to attack the rig before.
Ukraine and Russia have increased attacks in the Black Sea since Moscow pulled out of a key deal ensuring the safe navigation of cargo ships.