Opposition leader Alexei Navalny was sentenced to 20 days in jail on Monday for repeatedly violating Russian anti-protest laws.

Navalny has announced he will run for president next March, despite having a previous conviction which officially bars him from participating.

Tens of thousands of people have joined rallies in support of Navalny this month, including last weekend in the cities of Arkhangelsk and Orenburg. Previous rallies drew similar crowds in Murmansk, Yekaterinburg, Omsk, Novosibirsk, Vladivostok and Khabarovsk.

Navalny was detained outside his Moscow home late last week on his way to an event in central Russia’s Nizhny Novgorod.

A Moscow court ruled on Monday that he had repeatedly called for mass unauthorized public demonstrations. His campaign manager Leonid Volkov was also jailed for 20 days on the same charges.