(The Hill) – Border guards on Ukraine’s Snake Island on Thursday delivered a defiant message to a Russian warship demanding they surrender or be attacked.

The guards’ response to the request: “Russian warship, go f— yourself.”

Video of the encounter has gone viral on social media after it was shared by a Ukrainian news outlet. A Ukrainian official confirmed its authenticity to The Washington Post.

In video of the incident, you can hear the approaching ship warn the border guards. 

“I am a Russian warship,” the person said in a call to the the island, also known as Zmiinyi. “I ask you to lay down your arms and surrender to avoid bloodshed and unnecessary deaths. Otherwise, you will be bombed.”

After a brief discussion among the guards, they responded back to the ship.

The 13 guards were killed after Russia then opened fire on the island. Ukraine’s President Volodymyr Zelenskyy said the men “died heroically,” and would be posthumously rewarded with the title “Hero of Ukraine,” he wrote on his website, per Reuters.

Hundreds of troops were killed on the first day of Russia’s military assault on Ukraine.

Attention is now on the capital city of Kyiv as Russian forces close in on the populated area.