“Gazprom is not a competitive global firm,” the magazine cited one cable released by the whistle-blowing website as saying. “Gazprom is the successor to the Soviet gas ministry, and this is how it operates as well.”

“Gazprom is far away from its ambition to become the world’s most valuable company, with its fortunes taking a dramatic turn in the past year,” said another, dating from 2009.

“Its market value, production and sales have all collapsed since the start of the financial crisis.”

The diplomats also gathered from an insider that it took two full years for an international accounting firm to get a proper overview of Gazprom’s activities and its myriad subsidiaries from its books, the cables showed.

State-controlled Gazprom is the world’s biggest natural gas firm and controls around a quarter of the world’s reserves.

Critics have long accused Moscow of using the firm for political ends.

WikiLeaks began publishing in November some 250,000 leaked US diplomatic cables from 1966 to February 2010, revealing what it calls “the contradictions between the USA’s public persona and what it says behind closed doors.”

Some of the revelations have hugely embarrassed Washington, with the White House calling those behind the leaks criminals.