Lithuania blamed Moscow on Wednesday for the overnight attack by a hammer-wielding assailant on an exiled top aide to late Russian opposition leader Alexei Navalny outside his Vilnius home.

President Gitanas Nauseda said the attack on Navalny aide Leonid Volkov was clearly pre-planned and tied in with other provocations against Lithuania.

"I can only say one thing to (Russian President Vladimir) Putin - nobody is afraid of you here," Nauseda said.

Lithuania's State Security Department counter-intelligence agency said the attack was probably carried out to stop the Russian opposition from influencing Russia's presidential election.

Putin, in power since the turn of the millennium, is holding an election in coming days against token opposition to extend his rule by six more years.

The Kremlin views Navalny's team as "the most dangerous opposition force capable of exerting real influence on Russia's internal processes", the Lithuanian security agency said.

There was no immediate comment from Moscow on the incident.

Volkov himself also pointed the finger directly at Putin. In a post on Telegram, he said he had returned home on Wednesday morning after a night in hospital, having suffered a broken arm and injuries from about 15 hammer blows to the leg during the attack.

"This is an obvious, typical criminal ‘hello’ from Putin, from criminal Petersburg”, Volkov wrote.

"We will keep on working and we will not surrender”, Volkov added. "It's hard but we’ll handle it... It’s good to know I’m still alive."

In an interview hours before Tuesday night's assault, Volkov said leaders of Navalny's movement in exile feared for their lives.

"They know that Putin not only kills people inside Russia, he also kills people outside of Russia", Volkov saod in the interview. "We live in very dark times".

Earlier, former Navalny spokesperson Kira Yarmysh posted images of Volkov with a bruise on his forehead, blood coming from a leg wound, and a vehicle with damage to the driver's door and window.

"Volkov has just been attacked outside his house. Someone broke a car window and sprayed tear gas in his eyes, after which the attacker started hitting Leonid with a hammer," she wrote on social media website X.

Lithuanian Foreign Affairs Minister Gabrielius Landsbergis called the incident shocking and said the perpetrators must "answer for their crime". Lithuania's police commissioner Renatas Pozela said police were devoting "huge resources" to investigate the assault.

He insisted that the attack did not mean that the European Union and NATO country of 2.8 million people, which borders Russia and Belarus and has become a base for Russian and Belarusian opposition figures, was no longer safe.

"This is a one-time even which we will successfully solve... Our people should not be afraid because of this", said Pozela.

The US Ambassador to Lithuania, Kara McDonald, said on social media X she was "shocked" by the news of the attack on Volkov.

"His resilience and courage in the face of recent attempts to silence and intimidate him are inspiring. The Navalny team remains an outspoken voice against Kremlin repression and brutality," she said.

Navalny, President Vladimir Putin's most prominent critic, died last month in an arctic prison. Russian authorities say he died of natural causes; his followers believe he was killed by the authorities, which the Kremlin denies.