Arseny Roginsky, a prominent Soviet-era dissident who was a key founder of Russia's most prominent rights group Memorial, has died aged 71, the organisation said Monday.

Registered in 1992, Memorial is one of Russia's most respected human rights organisations and investigates everything from the Stalin-era Gulag to government death squads in Chechnya.

Roginsky, a former Soviet-era prisoner, died in an Israeli clinic following a "serious illness," a Memorial spokeswoman, Natalia Petrova, told AFP.

Memorial said in a statement it could not imagine itself without Roginsky, who was the organisation's chairman.

"Many years before Memorial was founded, he started the fight for historical truth and for human rights -- and was denied freedom for that," the organisation said.

"He continued this fight until his last day -- without him the work of Memorial all these years would have been impossible," it said.

Born in 1946 in Velsk, a town in Russia's northern Arkhangelsk region, Roginsky dedicated his life to documenting abuses and injustices in the Soviet Union -- and later Russia -- including Stalinist repressions.

He studied at the University of Tartu, in present-day Estonia, and edited anthologies on untold Soviet history called "Memory" that were published as "samizdat" -- without official sanction -- between 1975 and 1981.

He was pressured to emigrate in 1981.

He declined and several months later he ended up in prison after being charged with document forgery and receiving a four-year prison sentence.

He helped found Memorial in 1989, with Nobel Prize winner Andrei Sakharov, dedicated to research on Soviet purges as well as human rights violations in modern Russia.

- 'Symbol of his generation' -

Human rights activists said Roginsky's passing was a huge loss, with many highlighting his personal role in Memorial's activities including a highly charged annual reading-out of names of those killed in Stalin-era repressions in cities across the country.

The secretary general of the Council of Europe, Europe's top rights watchdog, Thorbjorn Jagland said in a statement that he felt "deeply saddened" at the death of Roginsky, whom he knew personally, calling him "a great figure of the modern history of his country."

Sergei Lukashevsky, director of Moscow's human rights Sakharov Centre, told AFP that "Arseny Borisovich was a symbol of his generation and his time."

"The son of a repressed person, he dedicated himself to studying the history of political repression and then found himself in a camp for his historical work," Lukashevsky said.

He called Roginsky a person "who united all" and said his death was a "huge loss for us."

The former head of Russia's Yukos oil company, Mikhail Khodorkovsky, also paid tribute, saying Roginsky as a former prisoner supported him when he spent a decade in jail.

Roginsky "brought more fairness to life," Khodorkovsky wrote on Twitter. "He was inspiring. He had been in jail himself and he supported me during my years in prison. He was a good man."

Russian authorities have steadily clamped down on rights organisations since the outbreak of street protests against strongman Vladimir Putin's return for a third term in the Kremlin in 2012.

Memorial, along with other rights groups, has been ordered to register itself as a "foreign agent" under a controversial 2012 law.