Navalny said on social media that Roskomnadzor, Russia's communications regulator, had warned him last week it would bar access to his site unless certain material was removed from it to comply with a court order reportedly obtained by billionaire Oleg Deripaska.
Roskomnadzor confirmed in a statement on Thursday it had ordered telecoms operators to block Navalny's site because the offending material was still there. It said Instagram had complied with a similar request to take down related material and that it was waiting for Google to delete a YouTube video.
The material it wants removed relates to an investigation disclosed by Navalny, who has been barred from running in next month's election, which alleges that Deripaska met Sergei Prikhodko, Russia's deputy prime minister, on a yacht belonging to the businessman off the coast of Norway in 2016.
Navalny questioned the ethics of the meeting in which he said the two men discussed US-Russian relations, and he posted what purported to be photographs of the encounter taken from the social media account of a young woman who was also on the boat.
He also issued a YouTube video to accompany his investigation that has been watched over 5 million times.
Deripaska, in a statement last week, accused Navalny and others of spreading lies about him and was reported to have obtained a court order in southern Russia to have the offending material removed.
"Outrageous false allegations appeared in social networks and mass media that I allegedly committed unlawful actions," the statement read.
"These allegations have nothing to do with reality, are the fruit of the imagination of a group of people, and the result of a planned campaign aiming to damage my reputation."