Jailed Kremlin critic Alexei Navalny said on Friday that he was halting his three-week hunger strike following advice from his doctors and thanked his supporters.

Navalny made the announcement after his personal doctors said in an open letter on Thursday he should "immediately" call off his hunger strike or they will "have no one to treat soon."

-Taking into account the progress and all the circumstances, I am beginning to end my hunger strike- President Vladimir Putin's best-known critic said in an Instagram post.

He said that the process would take him 24 days.

-They say it's even harder- he added.

On Wednesday, thousands of Russians took to the streets in dozens of cities across the country, after the West warned the Kremlin that it would face "consequences" in the event of Navalny's death.

Navalny announced a hunger strike in his penal colony on March 31, demanding to see an independent doctor for pain in his back and numbness in his arms and legs.

Navalny's personal doctors -- who have been unable to examine their patient in the prison -- last week said the results of his blood test showed he was in critical condition and was at risk of going into cardiac arrest at "any minute."

Navalny said that he was guided in his decision by the recommendation of his doctors, whom he "completely trusts", and the fact that some of his supporters also went on hunger strike in solidarity.

-Friends, my heart is full of love and gratitude for you, but I do not want for anybody to suffer because of me- he said.

Navalny added that he had been twice seen by civilian doctors and is getting medical tests.

He stressed that he still wanted to see an independent doctor, pointing to the numbness in his limbs.

Navalny was arrested when he returned to Russia in January after months recovering in Germany from a Novichok poisoning he blames on the Kremlin -- an accusation Moscow rejects.

He was sentenced to two-and-a-half years over an old fraud conviction and has been serving time in a penal colony about 100 kilometres (60 miles) east of Moscow.