Kroes took a swipe at the US following critical remarks made in a statement by Thomas Barnett, assistant attorney general at the US Department of Justice’s Antitrust Division on Monday.

I think it’s totally unacceptable that a representative of the US administration criticize an independent court of law outside its jurisdiction, competition commissioner Kroes said at a press conference yesterday.

It is absolutely not done, she added. The European Commission does not pass judgment on rulings by US courts, and we expect the same degree of respect from US authorities for rulings by EU courts.

Kroes’s transatlantic volley was tempered somewhat when EC president Jose Manuel Barroso, moments later, added: When we ask Microsoft to respect the competition rules, and when we enforce the competition rules, this is not against the US of America.

On Monday, Europe’s Court of First Instance rejected Microsoft’s appeal against a 2004 European Commission antitrust ruling, which fined the company $690m and placed restrictions on some anticompetitive business practices.

The court’s decision provoked an immediately unhappy response from the US. Barnett said that the DoJ is concerned that the ruling rather than helping consumers, may have the unfortunate consequence of harming consumers by chilling innovation and discouraging competition.

Barnett added that US antitrust laws are enforced to protect consumers by protecting competition, not competitors.

US courts recognize the potential benefits to consumers when a company, including a dominant company, makes unilateral business decisions, for example to add features to its popular products or license its intellectual property to rivals, or to refuse to do so, he said.

As well as the big fine, the 2004 European antitrust remedy went beyond the US’s, in terms of mandating the publication and licensing of technical interoperability information.

The EU remedy even obliged Microsoft to publish an entirely new version of its operating system, Windows XP/Vista N, which does not have a bundled Windows Media Player.

Windows N, priced the same as regular Windows, was a commercial failure, demanded in volume by neither consumers nor PC makers. WMP has a healthy 50% market share, much higher than when the EU antitrust suit started almost a decade ago.

But more recently, media players such as iTunes have gained significant ground on Microsoft even in the US, where there is no Windows N for sale.