What we know about the cause of Navalny’s reported death.

The Russian government has announced the death of Alexei A. Navalny without offering many details. Here is what we know about Mr. Navalny’s fate and what happens next:

Cause of death

In announcing Mr. Navalny’s death, Russia’s prison service said that he felt suddenly unwell during a walk. The medical workers who had arrived to attend to him in an ambulance had “performed all the required resuscitation procedures,” without success.

A doctor working near Mr. Navalny’s prison above the Arctic Circle told the independent Russian news outlet Mediazona that the closest ambulance team is 35 kilometers, or 22 miles, from the prison. By the time it would have arrived, a patient in severe distress would already be dead, said the doctor, who spoke on condition of anonymity. “Who were they resuscitating?” he added.

President Biden said at a White House appearance that, “We don’t know exactly what happened, but there’s no doubt that the death of Navalny was the consequence of something that Putin and his thugs did.”

The Kremlin spokesman, Dmitri S. Peskov, resorted to the government’s usual legalese in commenting on Mr. Navalny’s death, without offering additional details. Mr. Peskov said on Friday that the prison service “is carrying out all the checks and procedures in accordance with all the existing rules,” adding that the cause of death is being determined.

Some state media outlets went further, saying that Mr. Navalny died from a blood clot without providing the source of that assertion.

These claims could not be independently verified. But a former mid-ranking Russian prison official said they should be treated with caution. Anna Karetnikova, who oversaw pretrial detention centers in the Moscow region, said in her experience “blood clotting” was a common shorthand for lethal cases that prison authorities had no intention of investigating.

Next steps

Mr. Navalny’s team said on Friday that his lawyer was flying to the prison to establish the facts. They did not immediately confirm the death, adding that the family had yet to be officially notified.

Russian law states that families of inmates must be notified within 24 hours of their relative’s death.

The former prison official said that when a person dies in jail, protocol dictates that their body is taken immediately to a morgue. This means the lawyer is unlikely to find the body when they arrive at the prison, she added.

Under Russian law, the receiving morgue must perform an autopsy on Mr. Navalny’s body. The family is entitled to see the autopsy report, but they may not receive it for up to a week following the procedure, the former prison official added.

Alina Lobzina contributed reporting.