Prosecutors filed new charges Monday against the jailed Russian oil tycoon Mikhail Khodorkovsky and his business partner in an apparent move to head off any political threat from the nation's once-richest man before parliamentary and presidential elections.

Khodorkovsky, who angered President Vladimir Putin by funding opposition parties before 2003 parliamentary elections, has served nearly four years of an eight-year sentence on fraud and tax evasion charges and could be eligible for parole this year.

Khodorkovsky's lawyer, Yuri Schmidt, told The Associated Press that prosecutors in the Siberian city of Chita had indicted his client on charges of embezzling and laundering as much as $25 billion in illegal oil revenues.

Schmidt said the charges were "not simply absurd — they are insane. ... Whoever wrote them was either mad or drunk."

A Web site maintained by Khodorkovsky's supporters published a statement saying that prosecutors had also filed the same charges against his business partner, Platon Lebedev. The statement said both men insisted on their innocence.

Khodorkovsky, who is serving his sentence in a Siberian prison camp, could face up to 15 years if convicted on the new charges. This would keep him in prison beyond March 2008 presidential elections, which are expected to be won by whomever Putin names as his favored successor.

"Both Mr. Khodorkovsky and Mr. Lebedev will be eligible for release from prison later this year, after having served half their current sentences," Khodorkovsky's international legal team said in a statement.

"Fearing their release, the Russian government has brought these new charges now to keep our clients incarcerated at least through the next presidential election in 2008 and to stop them from effectively opposing the final destruction of the Yukos Oil Co., and the expropriation of its remaining assets, later this year," it added.

In Russia, prison terms on separate charges are not usually served consecutively; convicts are jailed for the longest term.

The founder of the now-bankrupt oil giant OAO Yukos, Khodorkovsky was convicted in 2004 on fraud and tax evasion charges following a politically charged trial. Lebedev also is serving eight years on these charges.

Analysts say he broke an unwritten pact with the Kremlin that Russia's vastly powerful business tycoons would keep out of politics. The campaign against him also reflected the state's drive to cement control over the economy's crucial oil and gas industry, according to observers.

Khodorkovsky and Lebedev were moved in December to a detention center in Chita for questioning, and brought to the regional prosecutor's office on Monday for their formal indictment amid tight security.

The two men are accused of defrauding Yukos through trading schemes that allowed its owners to skim off profits and subsequently launder the illegal funds through Khodorkovsky's Open Russia foundation.

Khodorkovsky, who was one of Russia's most powerful men after building up Yukos into the country's top oil producer, was detained at gunpoint in October 2003.

Prior to his arrest and the parallel tax probe that saw most of his oil empire transferred to a state company, Khodorkovsky was estimated by Forbes magazine to have a fortune worth $15 billion.

On Sunday, police briefly detained lawyers for Khodorkovsky and Lebedev in what his legal team decried as the latest example of official harassment.

Five lawyers acting for both men were detained by police at Moscow's Domodedovo airport in the evening as they were waiting to register for a flight to Chita, Schmidt said.

While the campaign against Khodorkovsky and the carve-up of Yukos, once the country's biggest blue chip company, shook faith in the rule of law, investors have set aside their concerns and are piling into Russia's oil boom economy.

The country's main stock market, which has soared since the tycoon's conviction, recently broke the $1 trillion mark in capitalization. Foreign direct investment last year stood at $31 billion.