Jailed Russian opposition figures have been reacting to the death of Alexei Navalny from their prison cells this week, with his former regional aide saying Wednesday that she was in mourning.

Navalny died at his Arctic prison last Friday. His widow Yulia Navalnaya has since accused President Vladimir Putin of killing him, while his mother has been unable to see his body.

Most Russian opposition figures have fled the country in past years, but some have stayed and are serving long prison terms.

Censorship is not allowing me to say everything that I think about the death of Alexei Navalny, Lilia Chanysheva, Navalnys representative in Bashkortostan who is serving seven years in prison, said in a message distributed by her associates.

I send my condolences to his close ones and parents. I am mourning, she said.

A day earlier, Vladimir Kara-Murza, who is serving a 25-year sentence - the harshest of all jailed opposition figures - said he was sure Putin was behind Navalnys death.

Kara-Murza said he foud out about the death when it was mentioned in passing during a radio report in his Siberian penal colony on Friday.

I definitely and firmly know one thing: the responsibility for the death of Alexei Navalny lies personally with Vladimir Putin, Kara-Murza said in a message from prison. Because Alexei was his personal prisoner.

The health of Kara-Murza, who is a dual UK and Russian citizen, has significantly deteriorated in prison.

Ilya Yashin, an opposition figure serving an eight-and-a-half-year sentence for denouncing the Ukraine offensive, also said he had no doubt that Navalny was killed on Putins orders.

In a message from prison Tuesday, Yashin also expressed fears for his own safety.

I am behind bars, my life is in Putins hands and it is danger, he said, adding that he was still determined to stick to my line.

Yashin was a close ally of Boris Nemtsov, the opposition figure who was gunned down outside the Kremlin walls in 2015.

As I stood over the body of Boris in February 2015, I swore to myself not to be scared, not to give up and not to flee, he said. (AFP)