YouTube on Thursday temporarily blocked a video posted by Russian opposition leader Alexei Navalny calling for a voters' strike, apparently because the video included "illegal" hashtags mentioning President Vladimir Putin.

Mr Navalny has announced a series of rallies across Russia on January 28 to call for a boycott of the 2018 presidential election, after Central Election Commission (CEC) refused to register him as a candidate in the race.

According to the politician, a video was posted with hashtags in Russian like #Navalny2018, #strike and #January28 among others.

“Just now we found out what was the formal reason [for blocking the video],” Mr Navalny wrote in his blog. “It sounds exotic – unlawful hashtags. We’ve never seen anything like this before.”

An hour and a half later, the video was available again. Mr Navalny's team removed the words “elections,” “boycott” and “rally” from the hashtags that accompanied it, along with the names of Mr Putin and CEC chair Ella Pamfilova, the Meduza news cite reported.

“How can these be declared ‘unlawful’? We’ve sent out requests [to clarify the situation] and are waiting for answers,” Mr Navalny wrote.

Later, Mr Navalny posted a screenshot of an email YouTube sent to one of his team members, apologising for blocking the video. YouTube said it was done inadvertently.