Russian police and investigators have raided the homes of several opposition leaders on the eve of a planned protest against President Vladimir Putin.

The Federal Investigative Committee says the searches targeted the organizers of an anti-Putin rally held last month.

They were Alexei Navalny and Sergei Udaltsov, who both spent 15 days in jail last month for demonstrating against Mr. Putin's inauguration; Ilya Yashin, an activist previously detained during a protest; and television personality Ksenia Sobchak.

Russia's main investigation agency said it planned to conduct about 10 searches Monday.

Navalny's spokeswoman called the action “rape of the Russian constitution.” She said the searches were meant to “prevent us from participating in tomorrow's action”.

The four Putin critics were also called in for questioning on Tuesday, making it difficult or impossible for them to attend the protest.

Opposition leaders are hoping to draw a large crowd for the protest, which comes days after Mr. Putin signed into law a bill dramatically raising fines for people involved in unauthorized rallies.

Organizers of illegal protests now face up to $30,000 in fines, while individual protesters could face a fine of up to $9,000 or as many as 200 hours of community service.

Mr. Putin was elected to a record third presidential term in March. He served from 2000 to 2008 before becoming prime minister under former president Dmitry Medvedev.

A constitutional amendment has extended the president's term in office to two consecutive six-year terms, meaning Mr. Putin could stay in power until 2024.