Mikhail Kasyanov, the former Russian prime minister, has for the first time disclosed details of a closed-door conversation he claims he had with Vladimir Putin in which the then president revealed political motives for the state’s legal pursuit of Mikhail Khodorkovsky, the jailed former Yukos tycoon.

Throwing his backing behind Mr Khodorkovsky’s suit in the European Court of Human Rights, Mr Kasyanov said he had laid out in an affidavit filed to the court in Strasbourg last week Mr Putin’s explanation in July 2003 for the rising state pressure on Mr Khodorkovsky and his Yukos oil company.