New York (AFP) - Kremlin critic Alexei Navalny's posthumous memoir will be released in October, chronicling his 2020 nerve agent poisoning and life in a brutal Russian prison camp, the US publisher of the book said Thursday.

The key opponent of Russian leader Vladimir Putin died in February in a penal colony, where he had been held in harsh conditions, sparking worldwide condemnation. 

Titled "Patriot," the book will be released on October 22, publisher Knopf said in a statement, while his widow confirmed the book would also be issued in Russian.

"It is the full story of his life: his youth, his call to activism, his marriage and family, and his commitment to the cause of Russian democracy and freedom in the face of a world super-power determined to silence him," Knopf said. 

"It expresses Navalny's total conviction that change cannot be resisted and will come."

'Halfway through life'

Navalny's widow, Yulia Navalnaya, who has taken over his mantle in exile, has accused Putin of killing her husband. She confirmed the book would be published in more than 10 languages, including Russian.

"This is not how I imagined Alexei would write his biography at all. I thought we'd be around 80 years old, and he'd be sitting at the computer by the open window, typing away," said Navalnya. 

"After the poisoning attempt in 2020, everyone insisted, 'Alexey, you should write a book.' He just shrugged it off. What kind of biography can be written at 44? It's barely halfway through life. 

"He wasn't rushing anyway -- there was still so much ahead. But things turned out differently. Horribly and very, very unfairly. It turned out there wasn't another half ahead."

Navalny began writing the memoir after the 2020 poisoning, which led to his hospitalization in Germany. He returned to Russia the next year, and was jailed.

'End of secrecy'

"Today is the end of secrecy. Alexei's book, which he started in Germany and finished in prison, will be published," said Navalny's spokeswoman Kira Yarmysh. 

"I'm looking forward to it. I can't wait for you to read it."

Navalny's death has robbed Russians opposed to Putin of their most charismatic figurehead at a time when authorities have crushed the last remnants of dissent.

The crackdown has intensified since the Kremlin launched its full-scale hostilities against Ukraine in 2022.

Putin, a former KGB officer, secured a new six-year term in power in the face of no genuine challenger at elections in March.

Putin for years refused to utter Navalny's name in public, but last month broke that pattern when he alleged he had approved an initiative to swap "Mr Navalny" for unnamed Russians in Western jails days before his death.

Navalny's team says Putin ordered his killing on the eve of a prisoner swap.

Navalnaya called the 71-year-old leader a "coward" for only uttering her husband's name after his death.

EU countries agreed to impose sanctions on 30 Russian officials over the death of Navalny.

But Navalny's allies said the limited targeting of a small number of prison officials was purely symbolic and would have no impact on the Kremlin.