The searches could lead to criminal charges, The New York Times reported.
Among 10 opposition figures whose apartments were searched are Aleksei Navalny, a blogger and anti-corruption crusader; prominent leftist Sergei Udaltsov; liberal organizer Ilya Yashin; and TV presenter Kseniya Sobchak, whose father, Anatoly A. Sobchak, was a mentor to President Vladimir V. Putin.
Vladimir Markin, a spokesman for investigators, said the four opposition figures have been summoned for interrogation Tuesday, which would likely prevent them from attending the noon protest.
The Kremlin has taken a harder line on huge anti-Putin gatherings. A dozen people face criminal charges stemming from a May 6 demonstration in which protesters and riot police clashed violently.
Putin signed a new law Friday dramatically increasing fines for protests -- to as much as $9,200 for participants and $30,600 for organizers.
But protest organizers say the higher fines and searches could lead to more people turning out for the protest Tuesday.
"What's taking place right now will have a very strong mobilizing effect and tomorrow we should expect many, many, many more people than were expected previously," said Sergei Parkhomenko, a journalist who has helped organize previous marches.
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