A group of Ukrainian border guards who were killed while defending a strategic Black Sea island on Thursday gave a defiant final message to their Russian aggressors, according to an audio recording of the incident.

       The 13 guards stationed on the remote Zmiinyi or Snake Island were informed by a Russian warship via loudspeaker that they should surrender or “be hit with a bomb strike”.

       “Russian warship, go f*** yourself,” was their leader’s reply.

       The audio recording was first obtained by Ukrainian news outlet Ukrayinska Pravda, and has been confirmed as authentic by Ukraine’s interior ministry. The guards involved have been hailed as heroes by president Volodymyr Zelensky.

       Snake Island, located off the country’s southeastern shoreline, was approached by the two Russian vessels on Thursday after Vladimir Putin declared the start of an invasion at 6am in Moscow.

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       “I am Russian warship, repeat I am Russian warship,” the advancing vessel announced. “Proposing to put down the arms immediately to avoid bloodshed and unjustified deaths.

       “In worst case, you will be hit with a bomb strike. I am repeating…,” they said, according to the translation by CNN.

       Two Ukrainian guards engage in a brief exchange — “should I tell them to go f*** themselves?” — before responding with: “Russian warship, go f*** yourself”.

       In a video message posted on Friday, Mr Zelensky confirmed the guards defending the island were among the 137 “heroes” to have been killed in the first 24 hours of Russia’s military operation.

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       Without confirming the exact number of guards who laid down their lives in the battle for the remote island, the president said that they died “heroically” and “did not give up”. They would be posthumously awarded Hero of Ukraine medals, added Mr Zelensky.

       “May the memory of those who gave their lives for Ukraine live forever,” he said.

       The island is now believed to be controlled by Russian forces.

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       The president said in his address that Ukraine will continue to defend itself, as he ordered a full military mobilisation to counter Russian aggression and banned all men aged 18-60 from leaving the country.

       “The fate of the country depends fully on our army, security forces, all of our defenders,” he said.