The auditor of Russian oil firm Yukos has withdrawn its reports over a 10-year period, casting doubt over information it was given by managers.
Yukos assets have been gradually auctioned off
PricewaterhouseCoopers (PwC) said it made the move after it became aware information given by former Yukos bosses "may not have been accurate".
Yukos' main shareholder criticised the decision, claiming PwC had come under political pressure from the Kremlin.
Yukos was declared bankrupt last year and its assets have been sold off.
Once Russia's largest oil firm, Yukos has been steadily dismantled after being accused of massive fraud and tax evasion by the Russian authorities.
Yukos has always maintained it was the victim of a concerted political campaign by the government, which wanted to discredit its executives and gain control of vital energy assets.
PwC said it was withdrawing its audit reports between 1995 and 2004 after new information came to light.
"PwC now believes information and representations which was provided by Yukos' former management may not have been accurate," it said.
PwC has been under pressure from the Russian authorities, which threatened not to renew its licence to operate in the country and raided its offices amid claims of underpayment of taxes.
But PwC - whose licence was ultimately renewed in April - said this had had no bearing on its decision.
GML, the largest shareholder in Yukos - condemned the decision - which may have a significant impact on its efforts to get compensation for Yukos assets which it claims were sold off illegally.
"I don't think anyone is going to believe this is anything other than bowing to pressure from the Kremlin," said Tim Osborne, managing director of GML.