The daughter of hunger-striking Kremlin critic Alexei Navalny has called on Russian authorities to allow a doctor to treat her father in prison, a day after a group of medical professionals warned he is at risk of kidney failure.

Mr Navalny, a fierce opponent of Russian President Vladimir Putin, started refusing food on March 31 in protest at what he said was a lack of proper medical care for acute back and leg pain provided by prison authorities.

Prison authorities say they have offered Mr Navalny medical care but the 44-year-old opposition politician has refused it and insisted on being treated by a doctor of his choice from outside the facility, a request they have declined.

“Allow a doctor to see my dad,” Mr Navalny’s daughter Dasha, a student at Stanford University, wrote on Twitter.

Allow a doctor to see my dad.

— Dasha (@Dasha_Navalnaya) April 18, 2021

A medical trade union with ties to Mr Navalny said on Saturday he was in a critical condition, citing medical tests it said showed that Mr Navalny’s kidneys could soon fail, which could lead to cardiac arrest.

A group of actors, writers, historians, journalists and directors, including Jude Law and JK Rowling, wrote an open letter to President Putin on Friday urging him to ensure Mr Navalny gets adequate medical attention.

A group of opposition regional politicians also called on Mr Putin on Saturday to make sure Mr Navalny is properly treated.

Speaking to the BBC's Andrew Marr, Andrei Kelin insisted Navalny's medical treatment would be "taken care of", and claimed the real purpose of his calls for medical help was to "attract attention".https://t.co/VJ1EcjxoIF

— Arzu Geybulla (@arzugeybulla) April 18, 2021

In a television interview with the BBC, Russia’s ambassador to Britain accused Mr Navalny of attention-seeking.

“He will not be allowed to die in prison, but I can say that Mr  Navalny, he behaves like a hooligan, absolutely,” Ambassador Andrei Kelin said in the interview, which was recorded on Friday and aired on Sunday.

“His purpose for all of that is to attract attention for him.”

Mr Navalny has said prison authorities are threatening to put him in a straitjacket to force-feed him unless he abandons his hunger strike.

Russia jailed Mr Navalny for two-and-a-half years in February for parole violations he insists were fabricated.

He was arrested in January when he returned to Russia from Germany, where he had been recovering from a nerve agent poisoning attack he blamed on Mr Putin.

The Kremlin has said it has seen no evidence he was poisoned and has cast Mr Navalny as a US-backed subversive on a mission to destabilise Russia.

-AAP