EU anti-trust regulators have carried out raids on some firms in the pharmaceutical sector on suspicions of collusion to delay the entry of generic drugs into the market, the European Commission said on Friday.

The Commission, which acts as the competition watchdog of the 27-nation European Union, said the raids took place Nov. 30 in several EU countries, but it did not identify the companies.

Drugmaker AstraZeneca confirmed it was a subject of the EU raid, which concerned heartburn drug Nexium, and that it was cooperating with EU authorities. Bayer, GlaxoSmithKline and Sanofi-Aventis said they were not affected.

"The Commission has reason to believe that the companies concerned may have acted individually or jointly, notably to delay generic entry for a particular medicine," it said in a statement, emphasizing that the inspections were a preliminary step in suspected anti-competitive practices.

"If confirmed, this could be a potential violation of EU antitrust rules that prohibit restrictive business practices," it said.

The European Commission said in October that it planned to review drug patent settlements struck by pharmaceutical firms to delay cheaper generics going to market, as part of its crackdown on illegal deals in the sector.

In a critical report on the sector in July last year, the Commission vowed to pursue drugmakers suspected of anticompetitive acts after an investigation found such delays had cost healthcare providers and consumers billions of euros. It later started probes into privately owned drugmaker Servier and several firms that make generic drugs and also raided several drugmakers, including Sanofi-Aventis, Novartis and Teva Pharmaceutical Industries.

In January this year, the EU watchdog sought details of deals between originator and generic pharmaceutical companies from July 2008 to December 2009. Its report showed there were fewer anticompetitive agreements.