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Alexei Navalny’s close ally Leonid Volkov has vowed to "never give up" fighting against Vladimir Putin, so the late Russian opposition leader’s "ultimate sacrifice" would "not be in vain".

Speaking after a brutal hammer attack in March outside his home in Lithuania, where he lives in exile, Mr Volkov told the ³ÉÈË¿ìÊÖ's Sunday with Laura Kuenssberg the message behind the assault was "we know where you live, we can kill you, we are after you".

Three people were arrested last month over the incident which Mr Navalny's long-time chief of staff believes was ordered by President Putin’s regime.

He said there was "no substitution" for Mr Navalny, but "everybody" saw his wife Yulia Navalnaya as the new "charismatic" leader of the opposition movement, even though "she never wanted to be in this public role".

Mr Navalny, 47, died suddenly in February while being held in an arctic prison colony on charges seen as politically motivated.

Mr Volkov said his friend’s death was an "open wound in our hearts".

He said: "We always knew we are fighting against, like a crazy, fascist dictator, who doesn’t recognise any red lines."

He said Mr Putin was "killing thousands of people", whether political opponents at home, in Europe or in Ukraine.

Mr Navalny’s aide warned there was "no one magic trick" that could oust the Russian regime.

He called on Western allies to send more arms to Ukraine and not to consider negotiation with Russia, despite its recent advances.

He said Mr Putin is "bluffing in a way to present himself like much stronger than he is, hopeful it will be enough to force Ukraine and its Western allies to enter some negotiation... don’t get bluffed".

Mr Volkov added there had to be "military pressure, economic pressure, political pressure, from inside, from outside" on Mr Putin.

He said: "If there are 50 things we can do, we have to do all 50 of them, if you do 49, that’s not enough, because that’s the greatest threat to the world that we’ve seen in 80 years."

Mr Volkov’s resolve is striking. He hardly flinches when he describes to me how his car window was shattered by his attackers in March, how they used pepper spray, and hammers to rain blows on his legs.

He almost seems surprised that people made a fuss of how he was violently targeted outside his own home, even though he has lived outside Russia for years for safety.

There is no question of him giving up his work for the Navalny Foundation, pushing for stronger sanctions against Putin’s allies, exposing corruption in the regime, seeking to exploit any weakness in the Kremlin and build political support.

Our politicians talk so often of the need to stand up to the Russian leader while wrangling over resources for defence, and extra weapons to support Ukraine.

But Russian opposition activists are living daily with danger.

Alexei Navalny was not the first casualty of the political fight against Vladimir Putin’s repressive regime. He may not be the last.

Watch the interview with Leonid Volkov on Sunday With Laura Kuenssberg live on ³ÉÈË¿ìÊÖ One and iPlayer from 09:00 BST on Sunday 19 May