President Joe Biden’s National Security Advisor Jake Sullivan said the United States government has told Russia “there will be consequences” if Kremlin critic Alexey Navalny dies in prison.

“We have communicated to the Russian government that what happens to Mr Navalny in their custody is their responsibility and they will be held accountable by the international community,” Sullivan told CNN on Sunday.

“In terms of the specific measures that we would undertake, we are looking at a variety of different costs that we would impose and I am not going to telegraph that publicly at this point, but we have communicated that there will be consequences if Mr Navalny dies,” he added.

The UK, France, Germany and the European Union have also expressed their concern over his treatment.

Navalny’s doctors say he “will die within the next few days” if not given urgent medical attention for acute back pain and leg numbness.

Russia’s ambassador to the UK has said that Navalny is attention seeking and “will not be allowed to die in prison”.

A prominent critic of President Vladimir Putin, Navalny, 44, was jailed in February for old embezzlement charges, which he claims are politically motivated.

He started a hunger strike on 31 March in protest at not being able to see his own medical team, and his doctors say recent blood test results indicate he could suffer kidney failure and go into cardiac arrest at any moment.