Police have raided the homes of prominent Russian opposition leaders and those of their parents in an apparent attempt to prevent their appearance at a large anti-Kremlin rally scheduled for Tuesday in the centre of Moscow, their representatives have said.

Alexei Navalny, an anti-corruption blogger, was the first to report via Twitter that police “nearly split the door in two” at 9:30am on Monday to search his flat.

Opposition TV personality Ksenia Sobchak, leftwing radical leader Sergei Udaltsov, and Boris Nemtsov, a former deputy minister, tweeted in rapid succession that their homes had also been targeted by police.

Ms Sobchak tweeted that police had “robbed” her home and humiliated her. Pro-Kremlin website Life News, citing investigators, reported that police found Ms Sobchak “in her negligee” and had confiscated more than €1.5m from a safe.

Vladimir Markin, a spokesman for the Investigative Committee of the Prosecutor’s Office, said investigators planned more than 10 searches on Monday, and that all searches were “done in strict accordance with procedure”.

Many of those searched were also summoned for questioning on Tuesday morning – coinciding with an opposition demonstration planned to start at noon.

Mr Markin declined to address why parents of activists were searched. The parents of Mr Udaltsov and opposition protestor Ilya Yashin, as well as Mr Navalny’s wife, were targeted, according to the activists.

A total of 50,000 people have been given legal permission to march through central Moscow along the picturesque “garden ring” of the city. The last such protest, on May 6, attracted 20,000-50,000 but ended in violence between protesters and riot police.

Monday’s searches was the largest pre-emptive action against dissidents since the beginning of the protest movement last December, and seemed to signal a new, hard-nosed attitude to demonstrations apparent following the return of Vladimir Putin as president last month.

Mr Markin said that among items confiscated during Monday’s searches were “agitation materials and literature containing anti state slogans”.

Yevgenia Albats, hosting a radio talk show on Monday evening in which she interviewed several of those targeted by the searches, said: “I have not heard the phrase ‘anti-state slogans’ in about 25 years, since about 1987.” She questioned whether the searches signalled a “Belorussification” of Russia under Mr Putin, referring to Russia’s authoritarian neighbour to the west.

“This is the biggest action yet against the opposition in terms of scale and also the most demented one,” Anna Veduta, Mr Navalny’s spokesperson, told the FT. She said searches were also conducted at the home of the parents of Mr Navalny's wife and in the offices of his corruption-fighting fund.

“In the end, it will probably be counterproductive and help us. The people will not accept such behaviour from the authorities.”

Mr Navalny, appearing later on Ekho Moskvy radio, said his flat had been searched for 13 hours. “It was clearly an attempt to intimidate us and paralyse our work,” he said. He and several others insisted they would nonetheless appear at the rally on Tuesday.

Last week, Mr Putin seemed to signal a crackdown was imminent when he pushed a law through parliament sharply raising fines for protest violations. Opposition leaders call it a ban, in effect, on unsanctioned demonstrations.

Alexei Kudrin, a former finance minister who has flirted with the opposition since he left government in September, said the searches and the new law pointed to the ascendancy of hardline elements in the Kremlin under Putin. 

“The searches of the opposition leaders on the eve of June 12, alongside the new law, will radicalise the protest and demonstrate the strengthening of the influence of radicals in the regime,” he said via Twitter.

Ms Veduta said the official reason given by police for the searches was an investigation into “mass disturbances” on May 6 when four police and dozens of demonstrators were injured in a melee. Since then, at least seven people have been arrested in connection with provoking the fights and attacking police with stones and sticks.

Later on Monday, Mr Navalny’s updates were no longer available on his Twitter site and his mobile phone went dead. Ms Veduta said that he was still in his flat along with police and they had confiscated all electronic equipment such as telephones and computers.

Left Front party leader Mr Udaltsovtweeted: “The search of my home has finished. They have taken a few bags of material evidence (papers, symbols, computers) and turned the whole apartment upside down.”

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