The European Union spends 200bn euros on drugs each year

GlaxoSmithKline, Pfizer, AstraZeneca and Sanofi-Aventis confirmed they were involved in the sector-wide investigation and co-operating fully.

EU Competition commissioner Neelie Kroes said the regulator suspected that drug firms had conspired to delay the introduction of cheap generic drugs.

However, the dawn raids were not based on specific information, the EU said.

Firms including Merck, Bayer Schering Pharma and Roche said they were unaware of their involvement in any raids.

US interest

The investigation aims to ensure that governments and consumers were getting new products and good value for money, Ms Kroes said.

"If innovative products are not being produced and cheaper generic alternatives to existing products are in some cases being delayed, then we need to find out why and, if necessary, take action."

Ms Kroes said that US competition regulators were also examining the issues.

She cited a 2005 ruling in which AstraZeneca was fined 60m euros (�45m; $88m) after the commission found the company had delayed market entry of rivals to an ulcer drug by misusing the patent.

EU figures suggest that Europe spends 200bn euros on medicines each year - the equivalent of 400 euros per person.