US remarks on Microsoft ruling 'unacceptable', says Kroes

"It is absolutely not on. The European Commission does not pass judgement on rulings by US courts and we expect the same degree of respect from US authorities for rulings by EU courts."

The commissioner's unusually harsh comments came as a reaction to a statement by the US Justice Department's top antitrust official, Thomas Barnett.

"We are concerned that the standard applied to unilateral conduct by the [EU court], rather than helping consumers, may have the unfortunate consequence of harming consumers by chilling innovation and discouraging competition," he said on Monday (17 September).

The remark was sparked by a judgment made earlier in the day by the European Court of First Instance - the EU's second highest court – which upheld an EU decision to fine software giant Microsoft €497 million for abusing its dominant market position and to order the US-based company to share information on its programming systems.

Ms Kroes is set to visit the US in the coming weeks where the issue is likely to come up.

The last time the two regions exchanged harsh comments about anti-trust regulation was in 2001 when the EU executive blocked a merger between US firms General Electric Co. and Honeywell.

The then EU anti-trust commissioner Mario Monti brushed off criticism from US president George Bush and other top US officials who accused the EU of "protectionism".