Russia on Monday dismissed concerns from Western countries over the health of jailed Kremlin critic Alexei Navalny, who began a hunger strike three weeks ago at his penal colony.

"The health of convicts in the Russia Federation cannot and should not be a topic concerning them," said Kremlin spokesman Dmitry Peskov, referring to Western countries that have stated that Russia was ultimately responsible for Navalny's condition.

Navalny announced a hunger strike late last month demanding proper medical attention for health complaints, including back pain and loss of feeling in his limbs.

The 44-year-old was imprisoned in February for more than two years on old embezzlement charges, weeks after he returned to Moscow from Germany where he had been recovering from nerve agent poisoning.

Peskov told reporters: "We do not monitor the health status of Russian prisoners".

Navalny's allies and medical professionals concluded last week that his condition was serious and that he could suffer cardiac arrest at any moment.

That assessment led his allies to call for demonstrations in more than three dozen cities across the country later this week.

The interior ministry on Monday, however, warned supporters of Navalny against taking to the streets and vowed to take action against participants in illegal demonstrations.

"Law enforcement agencies will not allow for any destabilisation of the situation and will take all necessary measures to maintain law and order in the regions of the country," the ministry said in a statement.

"Offenders will be detained and held liable according to the law."

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