WASHINGTON, April 18 (Aljazeera) - 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.

A doctor for Navalny, who is in the third week of a hunger strike, has said his health is deteriorating rapidly and the 44-year-old could be on the verge of death.

The prominent opponent of Russian President Vladimir Putin started refusing food on March 31 to protest against a lack of proper medical treatment for his leg and back.

“This latest threat from the US ratchets up other diplomatic problems that have fallen on the two countries,” Al Jazeera’s Mike Hanna reported from Washington, DC, citing recent sanctions imposed by the US on Russia.

On the question of what steps the US could take against Russia, Hanna said: “There are possibly steps like the expulsion of an ambassador. That would be an extreme diplomatic step taken by the US government.”