(BRUSSELS) - The European Commission on Monday announced the opening of a formal investigation into whether French pharmaceutical group Sanofi-Aventis illegally obstructed an inspection of its premises.

The European Union's top antitrust watchdog said the case centred around the group's "refusal to let inspectors examine and copy relevant documents until the French authorities produced a national search warrant," following the raid on its headquarters last January.

The raid on the company's headquarters in France in January was part of a wider EU antitrust probe into the pharmaceutical industry amid concerns about uncompetitive behaviour in the sector.

Between 15-18 January, the commission and French competition authority officials inspected the Sanofi-Aventis offices.

EU officials identified "certain documents which were relevant for the commission's competition sector inquiry" but Sanofi-Aventis refused to hand them over before the French authorities produced a national search warrant, the commission said in a statement.

EU rules empower the EU's executive arm to search company records and to take copies of documents during unannounced on-site inspections, the statement continued.

Concerned about a dwindling flow of new drugs and delays to generic products coming to the market, the commission's ongoing probe is aimed at determining whether patent settlements between firms break EU competition rules.

The EU regulators are also looking into whether drug companies illegally thwart the entry of rivals into their markets with artificial barriers such as misuse of patent rights or litigation.

Swiss Sandoz -- part of the Novartis group -- and British firms GlaxoSmithKline and AstraZeneca were also part of that enquiry.

Stressing that the probe "does not imply that the commission has proof of an infringement," the EU's executive added that there was no deadline to complete antitrust inquiries which could lead to a stiff fine.

Sanofi can look at a precedent in January when the European Commission slapped a 38-million-euro (56-million-dollar) fine on German energy group EON for breaking a seal on a room that contained confiscated papers.

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