A video investigation by Russia's leading opposition figure that claims President Vladimir Putin spent illicit funds on an extravagant Black Sea palace has reached more than 20 million people within a day of publication. Alexei Navalny's team released it after he was jailed on his return to Moscow. The investigation alleges the property cost £1bn ($1.37bn) and was paid for "with the largest bribe in history". The Kremlin denies the property belongs to the president. Claims that federal officials were guarding a vast palace complex on the Black Sea coast were "pure nonsense", spokesman Dmitry Peskov said. The Navalny investigation describes the property as 39 times the size of Monaco. The report was released on Tuesday, two days after Mr Navalny flew back from Germany and was arrested at the airport. He was placed in pre-trial detention for 30 days on Monday on a charge of violating probation terms for a suspended sentence for embezzlement that he maintains is politically motivated. A separate case against him was due to start on Wednesday but was postponed. The 44-year-old was almost killed in a nerve agent attack last August, which he blamed personally on Mr Putin. The Kremlin denies involvement. The opposition politician's allegations of security service involvement have, however, been backed up by reports from investigative journalists.