Fallen Russian oligarch Mikhail Khodorkovsky appeared in a Moscow court on Tuesday on new charges of embezzlement and money laundering in a case his lawyers say tests President Dmitry Medvedev's reform promises.

The fate of Khodorkovsky, an oil tycoon who fell foul of the Kremlin under former President Vladimir Putin and was jailed in Siberia for tax evasion and fraud, is being closely watched for any signs of a milder tone under Medvedev.

Police detained about 10 Khodorkovsky supporters outside the court as they shouted "Freedom to political prisoners, freedom to Mikhail Khodorkovsky," a Reuters reporter said.

Armed guards brought Khodorkovsky, wearing jeans and carrying a black briefcase, in a van to the Khamovnichesky court in Moscow -- the first time he has appeared in public in the capital since 2005. A supporter threw white roses towards him.

In a glass cage in the court, Khodorkovsky smiled and joked with business partner Platon Lebedev. He looked considerably older than when he last appeared in public.

A court spokeswoman said the hearing was closed to the public and reporters were allowed only briefly to film and photograph the defendants. Police sealed off the area around the courtroom and security was tight.

"This case is of immense importance because of what it will say to all of us about where Russia is going," Robert Amsterdam, a defence lawyer for Khodorkovsky, said by telephone from London before the hearing.

Khodorkovsky says he is the victim of corrupt officials who feared his political ambitions and wanted to carve up his YUKOS business empire, which produced more oil than OPEC member Qatar.

LAWYERS SAY KHODORKOVSKY IS POLITICAL PRISONER

The 45-year-old former businessman, once ranked as Russia's richest man, was brought to Moscow this month from a prison in Chita near the Chinese border to face the new charges at a preliminary court hearing in the capital.

Medvedev, a former lawyer sworn in as president last May, has demanded a clean-up of the Russian court system since Khodorkovsky's sentence and criticised high-level corruption.

Prosecutors say Khodorkovsky helped embezzle 900 billion roubles ($25 billion) and laundered 500 billion roubles ($13.9 billion), charges that could keep him in jail for 22 years more if found guilty.

Khodorkovsky's lawyers say their client is a political prisoner and the new charges are absurd. They say he is charged with stealing more oil from the YUKOS oil company that he controlled than it produced during the years in question.

Khodorkovsky became one of Russia's most powerful businessmen, widely known as oligarchs because of their immense wealth and influence, by buying state assets cheaply and trading commodities in the chaos after the Soviet Union collapsed.

His arrest in 2003 raised fears that the Kremlin would try to regain control of raw materials companies it had sold off. Khodorkovsky, who was convicted in 2005, says he is not guilty.

Kremlin critics say his arrest and the carve-up of his business empire marked a turning point in Putin's presidency by clipping the oligarchs' wings, allowing hardliners to get the upper hand and shelving reforms.