Kraft Foods and Nestle said today (11 February) that they are "co-operating" with the investigation into alleged price-fixing among chocolate producers in Germany.

The two food giants were among seven chocolate makers raided by German officials at dawn on Thursday as part of an investigation into alleged collusion.

The Bundeskartellamt, Germany's Federal Cartel Office, believes the rising cost of ingredients including cocoa and milk may have led chocolate makers to increase their prices.

"We suspect that there was collusion over a price increase at the beginning of 2008," the spokesperson added. "It makes sense that, when you see prices of raw materials rise, you raise your prices together - but it is not an excuse."

A spokesperson for Kraft, maker of Milka chocolate, refused to comment on whether the US firm had colluded with rivals to increase prices.

"We are co-operating with the authorities and we have given them what they wanted to see," sahe said. "We continue to wait for a timely close to the investigation."

However, she said the company had seen raw material costs rise by "between 30% and 100%" in the last 12 months.

"Milk powder, which is an important ingredient, has doubled in price," she told just-food.

A spokesman for Nestlé said the company had been trying to pass on its higher raw material costs on to consumers. However, he declined to comment on whether Nestlé had played a role in any price-fixing.

"We are co-operating with the authorities. This is at a very preliminary stage," he said.

Reports in Germany named companies including Mars as the other chocolate makers under investigation. Officials at Mars could not be reached for immediate comment.