The Dutch retailer Ahold, already battered by one of Europe's biggest corporate accounting scandals, has admitted further "intentional accounting irregularities" at one of its subsidiaries.
Ahold's Dutch chain Albert Heijn was a High Street favourite
The group also admitted it would miss the deadline for auditing its books.
The world's third-biggest retailer said it had unearthed a new $29m (£17.7m) accounting hole at its US retail business Tops Markets.
This follows the revelation that the US Foodservice division had overstated profits by $880m over three years.
Now we have to worry about the possibility that they might uncover more and more problems as they go through the books
Ahold, once one of Holland's most popular retailers, said the latest scandal had been discovered during accounting investigations into its various subsidiaries.
It will now miss the 30 June deadline to finish auditing its books, but said lending banks had granted an extension.
"This gives the impression that Ahold still doesn't have control of all its activities in the United States right now," said Paulo Nunes, a trader at Delta Lloyd.
More than half Ahold's sales are in the US, where its grocery chains include Tops, Stop & Shop, Bruno's and the US Foodservice group which delivers food to hotels, schools and restaurants.
US Foodservice profits were inflated between 2000 and 2002
The retailer said inquiries into other units had taken longer than expected and its accountant Deloitte & Touche was therefore behind schedule.
"The investigations completed thus far have also preliminarily identified or confirmed various accounting issues and internal control weaknesses," it said in a statement.
The latest scandal comes less than two weeks after Henry de Ruiter, chairman of Ahold's supervisory board, sought to reassure investors that he was "unaware of any other problems".
Analysts said they were "disappointed" by the latest findings, which dampened hopes that the worst was over for the group.
Ahold shares have lost a third of their value since the problems were first revealed in February: they fell another 1% on Monday.
"This is a little worrisome because up to now we had hoped that the problems in America were isolated to the US Foodservice and to [the Argentine unit] Disco," said one Amsterdam trader.
"But now we have to worry about the possibility that they might uncover more and more problems as they go through the books."