The European Commission has hit back at suggestions from Microsoft that Brussels will be to blame if competition concerns further delay the software giant's new version of its Windows operating system, Vista, in Europe.

"It is up to Microsoft to accept and implement its responsibilities as a near monopolist to ensure full compliance with EU competition rules and in particular the prohibition on abuse of a dominant market position," a commission spokesman said.

The reaction came after Microsoft said it was awaiting a reassurance from Brussels that Vista would not be targeted by competition authorities in a similar manner to its predecessors.

The two sides have been involved a long-running battle over the company's dominant grip of the software sector. Microsoft Windows is run on around 90 per cent of PCs and Europe has ordered the company to make the blue prints of previous versions available to competitors to allow them to develop products that will run smoothly with Windows.

In July, the commission threatened to ramp up its punishment of Microsoft yet further after fining the world's largest software developer a fresh €280.5 million (£194m) for breaking competition laws. Microsoft has now been fined a total of €780 million by the Commission after being found guilty of abusing its dominant market position in 2004.

Signalling that those hostilities are far from over, Microsoft yesterday suggested any commission demands on "additional design changes" could delay Vista.

Microsoft made the comments after members of the European Parliament wrote to the commission highlighting Microsoft’s reference to the EU’s regulatory activity as a "risk factor" to the product launch.

Vista has already suffered a string of delays. The consumer version will now miss the key Christmas period and be released in the new year, a pushback which is expected to hit PC manufacturers, chip makers and retailers as buyers postpone buying new machines.

Microsoft executives have told Times Online that the product will stick to its present timetable "touch wood".

In March, the commission sent a letter to Microsoft warning the company that it had concerns about Vista and giving warning that the product could not be launched in Europe with pre-installed programs that are sold automatically in the system’s package.

On July 12, Microsoft sent a proposal to the commission offering to change Vista.

The company's general counsel Brad Smith also sent a letter in early April on the "specific problem" of the inclusion of Portable Document Format (PDF) software.

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