Footage and audio of the incident Zmiinyi Island in the Odesa region appears to show the moment Ukrainian border guards stand their ground against a Russian warship.
The troops have been praised at home and around the world for their bravery after the defiant and expletive message against Russian President Vladimir Putin's forces emerged.
What happened on Snake Island?
The audio and video circulating on social media appears to show the warship hailing defending soldiers.
"This is a Russian military ship. I suggest you lay down your weapons and surrender to avoid bloodshed and unnecessary victims. Otherwise we will open fire on you."
The Ukrainian border guards appear to respond: "Russian military ship, go f*** yourself."
Ukrainian President Zelensky announced all soldiers – understood to be 13 troops – defending Zmiinyi Island were killed by Russian forces.
It is understood the two Russian warships involved in the shelling of Snake Island were the Vasily Bykov and Moskva.
Following the naval barrage, Russian troops landed on the island and seized the territory.
Ukraine crisis: What is NATO and what is its purpose, what are the NATO countries, and is Ukraine in NATO?
Where is Snake Island?
The remote outpost of Zmiinyi Island, also known as Snake Island, is situated in the western waters of the Black Sea near the Danube Delta.
It plays an important part in delineating Ukraine’s territorial waters in the Black Sea.
It has previously been the site of a border dispute between Ukraine and Romania between 2004 and 2009.
It fell to the International Court of Justice to resolve the dispute.
What has President Zelensky said about Snake Island?
Mr Zelensky said all border guards on the Zmiinyi island in the Odesa region were killed on Thursday,
“All the defenders of Snake Island died, but they did not surrender,” Zelensky said in a video posted on the social media platform Telegram, according to the New York Times.
He added that they would be named “heroes of Ukraine.”
Ukraine crisis: Where is the Chernobyl nuclear power plant, is it still operating, and what happened there?
Additional reporting from PA