Vladimir Putin has secret assets hidden abroad, leaked US cables from the former secretary of state Condoleezza Rice allege. Citing opposition sources, Rice said Putin refused to install a strong successor when he stepped down as president in 2008 because he was afraid he could become the target of “law enforcement investigations”.

Putin’s objective at the time was to secure his “alleged illicit proceeds”, the cables from her office said. Other classified cables referred repeatedly to the “secretive Swiss-based oil trading firm Gunvor” as an alleged source of Putin’s undisclosed wealth. The US ambassador in Moscow, John Beyrle, described the company as being closely connected to the Kremlin, and said its “secretive ownership is rumoured to include prime minister Putin”.

The allegations are likely to lead to fresh scrutiny of Putin’s personal wealth, following claims three years ago amid Kremlin infighting that he was Europe’s richest man.

One political analyst, Stanislav Belkovksy, estimated at the time Putin was worth at least $40bn. Putin ignored the story for several months, but eventually described reports that he had amassed a fortune through undisclosed links with business people as “just rubbish, picked out of someone’s nose and smeared on bits of paper”.

The Rice cable reported a conversation between an opposition leader, who was visiting Washington, and David Kramer, the then deputy assistant secretary of state for Europe and Eurasian affairs.

At this point Putin, who had already served two terms as president, was carefully weighing who to endorse as his successor. The obvious frontrunner appeared to be Sergei Ivanov, a charismatic, multilingual former KGB intelligence officer.

The opposition leader, however, told Rice’s office that Putin was “nervously seeking to secure his future immunity from potential law enforcement investigations into his alleged illicit proceeds”, and needed to find someone more pliable, the cable noted. “He commented that Putin was afraid of Ivanov, deeply distrustful, and that he needed a weaker figure to succeed him instead. “He argued that Putin understands that under the system he has created there is no real rule of law and that at any time anyone can be arrested or businesses destroyed.”—Dawn/Guardian News Service