Siemens's review of corruption allegations has identified more than 1.5 billion euros ($2.1 billion) in suspicious payments dating back 10 to 12 years, sources close to its supervisory board said on Thursday.
U.S. law firm Debevoise & Plimpton, which is conducting the probe for Siemens, has informed the company internally about the payments, the sources said.
The sum is higher than the amount the German industrial conglomerate had disclosed in December, when it said it had found 420 million euros in questionable transactions from 2000 to 2006.
The sources said the funds were primarily transfers and cash payments without receipts showing what the payments were for, but these were not necessarily bribes paid to win business.
In addition, the statute of limitations meant transactions made before 2000 were of little importance in terms of the criminal and tax codes in the United States and Germany, they added.
Siemens declined to comment.
Its shares rose 0.8% to 95.22 euros, slightly ahead of the German DAX blue-chip index.
The Wall Street Journal newspaper had earlier reported that an internal probe at Siemens had increased the amount of suspicious transactions to about 1.6 billion euros.
The article, citing people familiar with the matter, said the new estimate was disclosed last week to the company's supervisory board and spans transactions dating to the mid-1990s and extends beyond the telecommunications business.
Munich prosecutors are investigating several former Siemens managers on suspicion of bribery and breach of trust in connection with the allegations, which prompted the departure of its chairman and chief executive. Neither has been implicated.
The U.S. Securities and Exchange Commission is also probing the allegations, and could impose fines or sanctions if it determines wrongdoing.