The leader of Russian mercenary Wagner Group Yevgeny Prigozhin, who died in a fatal plane crash last week, has already been buried in St. Petersburg, his press office said Tuesday.

Prigozhin's press office said it was a small ceremony closed to the public.

"Yevgeny Viktorovich's farewell was held in a closed setting. Those wishing to say goodbye can visit the Porokhovskoye cemetery," it said in a statement, without specifying whether the mercenary chief killed last week in a plane crash had been buried.

Observers expect the grave could become a pilgrimage site for thousands of supporters of the controversial business owner and Kremlin loyalist-turned-traitor.

It had been unclear for days when and where the funeral would take place.

The cause of the crash of the private jet with 10 people on board remains unclear, though speculation was rife after President Vladimir Putin had pledged revenge against the mercenary leader for his attempted mutiny in June.