A Ukrainian soldier on a tiny island in the Black Sea didn't hold back when threatened with bombing by a Russian warship as Moscow

According to a purported audio exchange, as the Russians approached Snake Island, also known as Zmiinyi Island, the Russian officer says: "This is a military warship. This is a Russian military warship. I suggest you lay down your weapons and surrender to avoid bloodshed and needless casualties. Otherwise, you will be bombed."

A Ukrainian soldier responds: "Russian warship, go f*** yourself."

Those were the final known words heard from the island.

All 13 Ukrainian defenders were killed in a Russian bombardment Thursday, Ukrainian President Volodymyr Zelensky said.

"All border guards died heroically but did not give up. They will be awarded the title of Hero of Ukraine posthumously," Zelensky said.

Snake Island sits about 30 miles (48 kilometres) off the southern tip of the Ukrainian mainland in the northwestern Black Sea. It's about 185 miles (300 kilometres) west of Crimea, the Ukrainian territory that Russia annexed in 2014.

Though it is only about 46 acres (18 hectares) in size, a report last year from the non-partisan Atlantic Council think tank called it "key to Ukraine's maritime territorial claims" in the Black Sea.

Highlighting its strategic importance, Zelensky chose it last year as the spot for an interview with Ukrainian media in advance of a summit to try to reverse Russia's annexation of Crimea, the Atlantic Council report said.

Zelensky words to interviewers that day proved prophetic.

"This island, like the rest of our territory, is Ukrainian land, and we will defend it with all our might," he said.