Police have taken up positions near the church where Russian opposition politician Alexei Navalny is due to be buried in Moscow as his supporters estimate more than 1000 people have gathered to say goodbye to him.
Navalny, President Vladimir Putin's fiercest critic inside Russia, died at the age of 47 in an Arctic penal colony on February 16, sparking accusations from his supporters that he had been murdered.
The Kremlin has denied any state involvement in his death.
Tension is high before his funeral because the authorities have outlawed his movement as extremist and cast his supporters as US-backed troublemakers out to foment revolution.
Previous gatherings of his supporters have been broken up by force.
There was heavy security at the church in a southeastern Moscow suburb on Friday morning and it was surrounded by metal crash barriers with dozens of police vehicles parked nearby.
People carrying flowers arrived early to try to get in as the morgue holding his body began the process of releasing it to his relatives.
About an hour and a half before the service was due to begin, his allies said more than 1000 people had gathered near the church to say goodbye to him.
A religious service for Navalny is due at 2pm on Friday (2200 AEDT) in the Church of the Icon of the Mother of God in the Moscow district of Maryino where Navalny used to live.
He is scheduled to be buried two hours later at the Borisovskoye cemetery on the other side of the Moskva River.
The cemetery was sealed off with crash barriers on Friday.
Allies of Navalny outside Russia have called on people who want to honour his memory but cannot attend his funeral service to go to certain landmarks in their towns on Friday evening.
The Kremlin has dismissed statements by his allies as provocative and on Friday said any unsanctioned gatherings in support of Navalny would violate the law.
Navalny's wife Yulia, with whom he had two children, has said she is unsure whether the funeral will pass off peacefully or whether police will arrest attendees. She is outside Russia.
Navalny's mother Lyudmila, 69, is expected to attend his funeral. It is unclear who else will be allowed into the church for the service.
Navalny was a Christian who condemned Putin's decision to send tens of thousands of troops into Ukraine as a crazy enterprise built on lies.
In the run-up to his funeral, his allies accused the authorities of blocking their plans to hold a bigger civil memorial service and said unknown individuals had even managed to thwart their attempts to hire a hearse.
The Kremlin has said it has nothing to do with Navalny's funeral arrangements.
Navalny's allies - who have promised to livestream the day's events online - have accused Putin of having him murdered because the Russian leader could allegedly not tolerate the thought of Navalny being freed in a potential prisoner swap.
They have not published proof for that accusation but have promised to set out how he was murdered and by whom.
The Kremlin has denied state involvement in his death and has said it is unaware of any agreement to free Navalny.
His death certificate - according to allies - said he died of natural causes.
Navalny mounted the most determined political challenge against Putin since the Russian leader came to power at the end of 1999, organising street protests and publishing high-profile investigations into the alleged corruption of some in the ruling elite.
But a series of criminal charges for fraud and extremism - which Navalny said were politically-motivated - saw him handed jail sentences of more than 30 years and most of his supporters have either fled the country or are in jail.
Navalny decided to return to Russia from Germany in 2021 after being treated for what Western doctors said was poisoning with a nerve agent only to be immediately taken into custody.
Putin, who controls all the levers of state and is expected to be comfortably re-elected for another six-year term in two weeks, has yet to comment on Navalny's death and has for years avoided mentioning him by name.
