MOSCOW — An extraordinary wave of antigovernment protests swept across Russia on Monday, as thousands of demonstrators gathered in more than 100 cities to denounce corruption and political stagnation despite official attempts to stifle the expression of outrage.

Riot police officers in large cities and small detained hundreds of participants, with more than 700 apprehended in Moscow and 300 in St. Petersburg, according to OVD-Info, an independent organization that tracks arrests. There were reports of about 100 detentions elsewhere across Russia.

In Moscow, the police arrested the Kremlin foe and anticorruption crusader Aleksei A. Navalny, the main architect of the protests on Monday and similar ones in March, as he left his apartment to attend the demonstration downtown. A Moscow court quickly sentenced him to 30 days in jail for organizing an unauthorized protest.