Open Russia, the movement created by exiled former oil tycoon Mikhail Khodorkovsky, said Russian police on Thursday seized equipment and flyers printed for Saturday's anti-Kremlin protest.

Hours beforehand, Kremlin spokesman Dmitry Peskov described the intended protests as "illegal action" and warned authorities would make a "lawful reaction."

Open Russia foundation spokesperson Maria Baronova said police did not present a warrant and bureau personnel were told not to leave.

Almost simultaneously, three other Khodorkovsky-associated groups were put by Russian authorities on a register of banned "undesirable" organizations.

The search came a day after the office of Russia's general prosecutor said it had decided that the activity of the foundation's British arm was "undesirable."

Doused green

Navalny, meanwhile, was doused in a green fluid described as the Russian antiseptic "Zelyonka" by unidentified attackers outside his Moscow office. He was taken to the hospital for treatment.

Navalny, who hopes to run for president next year, said later in a Twitter message that his right eye had stung "like hell."

The fluid, which is hard to wash off, was used against Navalny in a similar incident last month, prompting supporters to appear in social media with green faces.

More anti-Kremlin protests planned

Planning for the opposition rallies on Saturday follows what was for many years Russia's biggest anti-Kremlin demonstrations in late March, called by Navalny over allegations of high-level corruption.

More than a thousand participants were arrested in Moscow alone, with some jailed for up to 25 days. Navalny was jailed for 14 days.

That turnout was prompted by a Navalny-authored documentary focused on Russian Prime Minister Dmitry Medvedev.

The premier replied that the claim of amassing a fortune was "nonsense."

Navalny's mini documentary drew more than 18 million views online.

ipj/sms(AP, AFP, dpa, Reuters)