Russia's top opposition politician Alexei Navalny died on February 16 at the Arctic prison colony where he was serving a 19-year term.

Here is what we know so far about the death of the 47-year-old head of the Anti-Corruption Foundation, an outspoken critic of President Vladimir Putin.

Died 'after a walk'

Russia's federal penitentiary service said Navalny fell ill after going for a walk.

"Navalny felt bad after a walk, almost immediately losing consciousness. Medical staff arrived immediately and an ambulance team was called," the prison service said in a statement.

"Resuscitation measures were carried out that did not yield positive results. Paramedics confirmed the death of the convict. The causes of death are being established," it added.

Russian news agencies reported that medics from a nearby hospital were called seven minutes later and spent half an hour trying to resuscitate Navalny.

Russia's Investigative Committee have opened an investigation into the death.

A lawyer for Navalny and a regional court said he had actively participated in a video legal hearing on Thursday, the day before he died, when he did not appear to have any health complaints.

Row over body, funeral

Navalny's mother travelled to the remote Arctic region a day after his death.

She was not allowed to see the body for several days despite repeated requests.

"It's obvious that the killers want to cover their tracks and are therefore not handing over Alexei's body, hiding it even from his mother," Navalny's team said in a post on Telegram.

She said she was finally shown her son's body on February 21 and that local investigative officials were trying to pressure her into holding a "secret" funeral.

Navalny's spokesperson Kira Yarmysh said on February 24 that the body had finally been handed over to his family.

Navalny's supporters said no venues in Moscow were willing to hold a civil public farewell ceremony and even reported problems in finding a hearse to carry the coffin.

International outrage

Western governments have been quick to hold the Kremlin responsible but have stopped short of making direct accusations of involvement.

"Make no mistake, Putin is responsible for Navalny's death," US President Joe Biden said.

Biden later met with Yulia Navalnaya and the couple's daughter, Daria.

French President Emmanuel Macron said that "in today's Russia, free spirits are sent to the gulag and condemned to death".

China's foreign ministry declined to comment, saying it was "Russia's internal affair." 

Spontaneous gatherings occurred outside Russian embassies in capitals across Europe, with protesters blaming Putin for his death.

In Russia, a human rights group said some 400 people were detained at tributes for Navalny in the days after his death.

Many mourners placed flowers at two monuments in Moscow for victims of Soviet repression amid a heavy police presence.

Prison colony

Navalny had been detained in Russia since January 2021 when he was sentenced to a prison colony for "extremism". That term was extended to 19 years in August last year.

It was just the latest in a string of jail terms for charges that included embezzlement.

He had spent most of his detention at the IK-6 penal colony in the Vladimir region, some 250 kilometres (155 miles) east of Moscow.

In December he disappeared for more than two weeks. At the end of that month it was revealed that he had been moved to the notorious IK-3 colony at Kharp in the Arctic.

Navalny said on social media on December 26 that he was "fine" after a "pretty exhausting" 20-day transfer to the remote prison.

The prison's nickname is "Polar Wolf".

- Poison before prison -Navalny mobilised huge anti-government protests before being jailed in 2021, after surviving an attempt to assassinate him by poisoning.

Starting out as an anti-corruption campaigner in 2007, Navalny led huge protests in 2011-12 and received his first conviction in 2013 for embezzlement. He denied the charges.

After being barred from the 2018 presidential election, Navalny was admitted to hospital in Siberia in August 2020 after losing consciousness during a flight.

He was transferred to a Berlin hospital where tests showed he was poisoned with Novichok, a Soviet-era nerve agent. Navalny blamed Putin for the poisoning. The Kremlin denied the accusation.