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Three people have been arrested over an attack on a senior aide to the late Russian opposition leader Alexei Navalny.

Leonid Volkov said his arm was broken outside his home in Lithuania's capital city, Vilnius, in March.

Poland's prime minister the person who allegedly ordered the attack was "a Belarusian working for the Russians".

Two Polish citizens linked to football ultra fan groups are accused of carrying it out.

Lithuanian intelligence originally said the attack was likely "Russian organised".

At a press conference on Friday, Lithuania's President Gitanas Nauseda confirmed the arrests, thanking Polish authorities.

He expressed his gratitude to President Andrzej Duda and in a , formerly Twitter, warned the organisers of the crime to "not try to repeat it".

Two Polish citizens were being held in Poland's capital Warsaw, after being detained on 3 April, the Lithuanian prosecutor's office said.

They added that the attack was fuelled by Mr Volkov's "beliefs and his political activities".

The 43-year-old was Navalny's chief of staff and has lived outside Russia for some years due to safety concerns.

Polish police said the detained men were wanted under a European Arrest Warrant, and were being held at Warsaw-Praga district prosecutor's office.

Meanwhile, Poland's Prime Minister Donald Tusk said a Polish man was arrested and charged separately for planning to co-operate with Russian intelligence services, to aid an attempted assassination of Ukraine's President Volodymyr Zelensky.

"There will be no leniency for collaborators of the Russian services," Mr Tusk said. "We will burn down every betrayal and attempt at destabilization."

Giving his reaction to the arrests, Mr Volkov said: "I don't know any other details yet, but I can say I have seen how energetically and persistently the Lithuanian police have worked over the past month on this case, and I am very glad that this work has been effective."

Back in March, the activist said the attack was "an obvious, typical, gangster greeting from Putin, from bandit St Petersburg" - but gave no more details.

"Everything happened in silence... of course this is a clear political attack, there is no doubt here," he added.

Kremlin officials declined to comment on the arrests during a news conference on Friday.

Mr Volkov was briefly hospitalised after the attack, which took place as he arrived at his Vilnius home by car on 12 March.

Pictures were posted on social media at the time, by another member of the Navalny team, showing Mr Volkov with bruising to his head and a bloodied leg. He said he had been pepper sprayed and hit with a hammer multiple times.

Russia's late opposition leader Alexei Navalny died suddenly in prison in the Russian Arctic in February.

This week, his widow Yulia Navalnaya said Mr Volkov's attack had prompted her to hire a bodyguard.

"Today they attacked Leonid, tomorrow they'll break into the house," she , adding that Mr Volkov's wife was in their home "with their little kids" at the time.

Ms Navalnaya said neither she nor her late husband used to have security, "but when you're too cavalier, you can make a wrong move".