Navalny has become the leader of the disparate opposition groups which oppose Putin, a former KGB spy who has ruled Russia since 1999 when Boris Yeltsin handed him power. 

"Putin is an old fashioned demagogue but with a background in the secret service so he is very well equipped to be a tyrant," said John Taylor, a British man who joined the protest holding a white plastic lavatory brush. 

The lavatory brush has become a symbol of protest in Russia as Navalny's video investigations alleged that Putin had opulent lavatory brushes installed in a palace. Putin has repeatedly dismissed Navalny's claims as nonsense, as has the Kremlin. 

Mostly Russian protesters outside the embassy chanted "Free Navalny, Free Russia" in both Russian and English while some held a giant picture of Navalny, 44, and others a placard which read "Today Navalny, tomorrow you". 

"We all want Alexei Navalny to be freed and to receive medical help," Marina Litvinenko, the widow of ex-KGB spy Alexander Litvinenko, who was poisoned with a rare radioactive isotope, polonium-210, in 2006. 

"Mr Putin - the people don't want you." Litvinenko told Reuters. 

Other protesters included former Russian mobile phone entrepreneur, Yevgeny Chichvarkin, who fled Moscow in 2008. 

"We came here to show our support for Alexei," Chichvarkin said. "He is the proper leader of the opposition and what has happened to him in Russia is completely unacceptable." 

Navalny travelled to Germany last August for treatment following a nerve agent poisoning attack he blamed on Putin. He was arrested in January when he returned to Russia and jailed for 2-1/2 years in February for parole violations he said were fabricated. 

The Kremlin has said it has seen no evidence he was poisoned and has denied any Russian role if he was.