Russian police forcibly detained over 800 people attending a protest in Moscow on Saturday to demand free elections, including prominent activist Lyubov Sobol, after authorities warned the demonstration was illegal. Police removed Sobol, an ally of jailed opposition politician Alexei Navalny, from a taxi and bundled her into a van minutes before the start of what anti-Kremlin activists described as a peaceful walk to protest against the exclusion of their candidates from an election next month. In another blow to Navalny, Russian investigators opened a criminal investigation into the alleged laundering of 1 billion roubles ($15.3 million) by his anti-corruption foundation. Navalny and his allies say the foundation, which has published a slew of embarrassing investigations into government officials, is transparently financed from public donations. OVD-Info, an independent monitoring group, said police had detained 828 people in Moscow on Saturday, in some cases beating them with truncheons as they lay on the ground. Reuters reporters witnessed dozens of arrests. In one case police carried off a man as he clung upside down to his bicycle. Police said they had detained 600 and that 1,500 had attended the protest, though footage of demonstrations which flared in different parts of Moscow suggested many more had taken part. Opposition activists later posted screen shots online of police reports suggesting around 10,000 had attended. Saturday's protest was smaller than one a week earlier, but underlined the determination of some Kremlin critics -- especially younger people -- to keep pressing to open up Russia's tightly-choreographed political system. Many but not all of those detained were later released by police, including Sobol who was fined 300,000 roubles ($4,596) for violating Russia's tough protest laws. The focus of protesters' anger is a prohibition on a number of opposition-minded candidates, some of whom are allies of Navalny, from taking part in a September election for Moscow's city legislature. That vote, though local, is seen as a dry run for a national parliamentary election in 2021. -Reuters