The trial of Russian oligarch Mikhail Khodorkovsky shows the Kremlin preserves a "cynical system where political enemies are eliminated with impunity", US diplomats say in classified cables released by WikiLeaks today.

Attempts by the Russian government to demonstrate the rule of law is being respected during Khodorkovsky's prosecution are "lipstick on a political pig", says a communique to Washington from the US embassy in Moscow in December 2009.

Khodorkovsky, 47, an oil tycoon who was arrested in 2003 and sentenced to eight years in jail for fraud two years later, will appear in court in Moscow today to hear the verdict in his second trial on embezzlement charges. Supporters of the man once Russia's richest say the Kremlin ordered the prosecutions in revenge for his funding of opposition parties.

Khodorkovsky could get up to six more years in jail at the end of his current sentence in October next year, if convicted. His business partner, Platon Lebedev, faces the same punishment.

While US officials have already publicly criticised the trial, which began in March last year, the baldness of the language in the secret cables is striking.

Writing to Washington in December last year, a political officer in the US embassy in Moscow noted that one international legal expert believes the trial judge is trying to give Khodorkovsky's defence lawyers a chance. However, in a withering assessment, the officer adds: "The fact that legal procedures are apparently being meticulously followed in a case whose motivation is clearly political may appear paradoxical.

"It shows the effort that the GOR [government of Russia] is willing to expend in order to save face, in this case by applying a superficial rule-of-law gloss to a cynical system where political enemies are eliminated with impunity."

The diplomat's assessment reaffirms those made in US cables released earlier by WikiLeaks, in which Russia is described as a kleptocratic "mafia state" in which officials, oligarchs and organised crime are inextricably linked.

It refers obliquely to a meeting in 2000 when Vladimir Putin, then still president, met Khodorkovksy and 20 other oligarchs and reportedly warned them to stay out of politics in return for their businesses being left in peace.

"There is a widespread understanding," writes the diplomat, "that Khodorkovsky violated the tacit rules of the game: if you keep out of politics, you can line your pockets as much as you desire."

The officer adds: "It is not lost on either elite or mainstream Russians that the GOR has applied a double standard to the illegal activities of 1990s oligarchs; if it were otherwise, virtually every other oligarch would be on trial alongside Khodorkovsky and Lebedev." At his annual TV question and answer session earlier this month, Putin, now prime minister, brushed off criticism off the trial. Russia had "one of the most humane court systems in the world". He added: "It is my conviction that a thief should be in jail."

Khodorkovsky's Yukos oil company was confiscated and sold to state-controlled firms after his conviction. He fired back on Friday in a letter to Putin published in a Russian newspaper. He pitied Putin, a "not-young person, so upbeat and so alone before a boundless and remorseless country". The premier, said Khodorkovsky, was helmsman of a galley which "sails right over people's destinies" and "over which, more and more, the citizens of Russia seem to see a black pirate flag flying".

Khodorkovksy also mocked Putin's recent television appearances with his new dog, Buffy. "Love of dogs is the only sincere, good feeling that pierces through the icy armour shell of the 'national symbol' of the beginning of the 2000s," he wrote. "A love of dogs has become a substitute for a love of people."

The verdict in Khodorkovsky's trial was due on 15 December but a note pinned on the door of Moscow's Khamovnichesky court that morning said it had been delayed until tomorrow. Some analysts believe the delay was deliberate, in order to deflect media attention over the holiday period.

Khodorkovsky and Lebedev are accused of embezzling the entire crude oil production of Yukos over a six-year period.

A source close to Khodorkovsky predicted he "would likely remain in prison as long as the Putin administration is in power,", according to the US cables released today. Putin is widely expected to return as president in 2012 and could serve two more terms, until 2024.

The judge is expected to spend several days reading the verdict.