“His condition has not changed,” Mr. Kara-Murza’s wife, Evgenia, who lives with their three young children in the United States, wrote in an email to reporters. “The hemodialysis treatment he is undergoing has no effect, and his condition remains very grave. He has not regained consciousness.”

In an interview on Wednesday, Ms. Kara-Murza said she feared her husband had been poisoned and that he remained in danger as long as he stayed in Russia.

“In order to get an independent medical assessment of his condition I have requested an urgent medical evacuation to a medical center in Europe or Israel where full toxicology testing and treatment can be done,” she said. “Thank you for your support and prayers.”