A close ally of late opposition leader Alexei Navalny urged Russians on Tuesday to turn out in big numbers for an election day protest against President Vladimir Putin next month that Navalny had called for shortly before he died.

The Kremlin warned there would be legal consequences for anyone who heeded what it called a provocative call from people it has labeled as dangerous U.S.-backed extremists.

In a post on social media Feb. 1, Navalny had urged Russians to register their protest by all turning out to vote at the same time, at noon March 17. Navalny died in an Arctic penal colony Feb. 16.

Navalny's ally Leonid Volkov, in a video published on YouTube, said the protest call was "Navalny's direct political testament," and the last call to action that he issued.

"Now this is no longer just a political action aimed at overcoming political loneliness and isolation. Now this is a rally of mourning and a civic memorial, an action in memory of Navalny, who asked us to hold it," he said.

"People will thus fulfill the last will of Alexei Navalny, so this is very important. Do it. And in the time remaining before the election, convince as many people as possible to do this."

Kremlin spokesman Dmitry Peskov told reporters Navalny's supporters were well known for their "provocative" appeals to break the law, and that there would be consequences for those who heeded such appeals.

"These people, so-called supporters (of Navalny) are well know for their provocative calls - to break the laws of the Russian Federation," Peskov said.

"This is a very harmful practice and has legal and law enforcement consequences for those who respond to these calls."

Navalny had called for the "Noon against Putin" protest as a way for people to mount a show of resistance without risking arrest, as they would simply be queuing up to vote legally.

Putin is assured of winning a new six-year term in the election. Two anti-war candidates have been disqualified on technical grounds and none of the remaining three candidates is critical of the president.