Moscow's prosecutor on Monday submitted a huge amount of new material to a court hearing a request to outlaw jailed Kremlin critic Alexei Navalny's political movement, Navalny's lawyers said.

The court is considering the prosecutor's request to declare Navalny's anti-corruption foundation and regional campaign groups as "extremist", a major escalation in a crackdown on supporters of President Vladimir Putin's staunchest critic.

Navalny and his allies deny the allegations, which they have cast as an attempt to try to blunt their political opposition to the ruling United Russia party ahead of parliamentary elections in September.

Navalny's lawyers posted photographs on social media of the prosecutor's new material -- six gigantic wads of A4 paper.

The next court hearing will take place on June 9, the lawyers said.