A Moscow court has ordered the head of Russian oil giant Yukos, Mikhail Khodorkovsky, to be kept in prison after he was charged with offences including defrauding the state out of $1bn.
Khodorkovsky and his company have been targeted by prosecutors
The move came hours after his dramatic arrest at a Siberian airport by agents of the security police (FSB).
Mr Khodorkovsky, who is believed to be Russia's richest man, was flown back to Moscow for questioning and charged with several offences, including tax evasion and fraud.
Critics say the investigation into his company is an attempt by the Kremlin to assert its power over business tycoons and keep them out of Russian politics.
Prosecutors argued that his detention was necessary because he had ignored a summons for questioning on Friday.
They have been investigating allegations of tax evasion and theft of state property by Yukos executives.
The Russian Interfax news agency quoted an official at the
prosecutor's office as saying: "The head of Yukos has been charged with a series of crimes, including large-scale theft and tax evasion, both personally and by the company."
Mr Khodorkovsky was flying to the Russian Far East on a business trip when his plane landed at Novosibirsk airport for a refuelling stop before dawn.
Personal wealth: $8bn
26th in Forbes' billionaires list
1987: Founded Menatep bank
1995: Bought Yukos at auction
Supports opposition Yabloko and Union of Rightist Forces
"They rushed to the plane, shouting 'FSB. Lay down your weapons or we will shoot!'" Yukos spokesman Alexander Shadrin said.
Yukos rejected the prosecutors' claims that Mr Khodorkovsky had ignored the summons.
Mr Shadrin told the Associated Press that Yukos had received a summons, but the company had written back to say that he was on a business trip and would be unable to appear.
Yukos, Russia's largest oil group, is merging with rival Sibneft, to create one of the world's top oil producers.
Two Yukos executives are facing criminal charges, including Platon Lebedev, the group's chief financier, who is in jail waiting for trial on charges of defrauding a state company in 1994.
Yukos was raided by agents in July
Earlier this month tax-evasion charges were filed against Vastly Sharkhnovsky, who is responsible for the auditing of operations.
Mr Khodorkovsky, who has an estimated personal fortune of $8bn, has already been summoned and interrogated by prosecutors twice over the case.
Police first raided Yukos offices in Moscow in July, spending nearly 17 hours searching through computer
Prosecutors have also searched companies owned by Yukos the homes of shareholders.
The BBC's Sarah Rainsford in Moscow says many Russians believe the probe into Yukos is politically motivated, pointing out that it only began after Mr Khodorkovsky began financing opposition parties.
The Russian authorities have been seeking the extradition of other high-profile Russian businessmen who now live abroad.
These include Boris Berezovsky, who has been granted asylum in the UK, and Vladimir Gusinsky, who managed to argue against being sent back to Russia in both the Spanish and Greek courts.