Allegations of torture in custody have been made by the legal team representing the executives of the Yukos oil giant who are imprisoned in Russia.

According to the defence lawyers, Alexei Pichugin, the imprisoned ex-head of security at Yukos, has been injected with mind-altering drugs in an attempt to get him to testify against Mikhail Khodorkovsky, the former chief executive of Yukos, who was arrested last month.

The charge is contained in a damning dossier prepared by the international defence team that is working for Mr Khodorkovsky, Mr Pichugin and Platon Lebedev, the ex-president of Yukos, who is also in custody. Mr Khodorkovsky, Russia's richest man, has become a political figure, who is even considering standing for the presidency.

The document, from Amsterdam & Peroff, a Toronto-based law firm, said the Yukos case is "a watershed event that has taken on universal and historic significance".

The dossier alleges wide scale abuse of the rights of the three defendants. The lawyers are seeking to bring other countries to support the cause of Mr Khodorkovsky, Russia's leading "oligarch", over tax evasion and fraud charges.

The defence document is an "urgent appeal to the international community" to intervene. The defence team also declared that the case cannot be seen in isolation from a more general attack on civil liberties in Russia and that other businessmen and foreign investments in the country are in danger.

The dossier accused the prosecution of violating human rights guaranteed by the Russian Constitution "in its rush to prepare a series of political show trials" ahead of upcoming parliamentary and presidential elections.

According to the lawyers, the Russian courts that have been hearing the Yukos cases against the three men are in the grip of the Kremlin, which is generally thought to be behind the campaign against Mr Khodorkovsky.

The defendants' "ability to receive a fair and impartial judgment from Russia's government-controlled court system is virtually non-existent".

Robert Amsterdam, Mr Khodorkovsky's lawyer, said: "There is now an atmosphere in Moscow that some say didn't even exist in Soviet times, hard as that is to comprehend."

The oil tycoon fell foul of the Russian government by funding parties opposed to the administration of President Vladimir Putin and speaking out against the authorities, which he accuses of leading the country into authoritarianism.

European Union officials met Mr Putin yesterday, with the Yukos case expected to be brought up by the European side.

The defence document said that the pre-trial hearing has taken place in secrecy, with even the lawyers of the three men sometimes excluded. The fear is that the full trials, when they take place, will also be behind closed doors.

The lawyers said they have not been given proper access to their clients and that the Moscow office of Anton Drel, the main local attorney of Mr Khodorkovsky, was raided last month by two dozen officers of the FSB, the successor intelligence service to the KGB. Hundreds of files and other sensitive documents relating to the case were taken away, including the detailed legal defence strategy that had been prepared.

According to the lawyers, both Mr Lebedev and Mr Pichugin, have been treated "inhumanely".

Mr Lebedev, who has a heart condition, has been refused access to proper medical attention. In addition, document said: "The FSB has tortured Mr Pichugin and injected him with psychotropic drugs.... The FSB is brutalising Mr Pichugin with a view to turning him into a witness who will testify against the principals."

There is no way of verifying these allegations. The Russian embassy in London said the case was a "purely judicial matter" and it therefore could not comment.