"We have submitted proposals and we are awaiting a response from the EU Commission," a spokesman said.

In 2004, Brussels found Microsoft guilty of abusing its market dominance and fined it 497m euros ($655m; £340m).

If the EU considers Microsoft's response to have fallen short, it could hit the firm with daily fines of $5m.

EU scrutiny

"Contacts continued between the European Commission and Microsoft until late last night, and the Commission will now carefully analyse what's on the table," a spokesman for the Commission said.

EU regulators would now assess "whether or not we consider that Microsoft has complied with the March 2004 decision", he said.

The 2004 ruling focused on Microsoft's behaviour in two key markets: servers, the computers which sit at the heart of networks, and media software.

The European Commission told Microsoft that it would have to open up its core software systems to rivals, making it easier for them to build products which would work with its Windows operating system.

It also ordered Microsoft to provide a version of Windows without its own Windows Media Player, to give rival software makers a chance to compete and computer makers the option to supply PCs with the media software of their own choosing.

Final plan

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The EU has the power to fine Microsoft up to 5% of its daily global turnover for each day that the antitrust ruling is not applied to its satisfaction.

The 1 June deadline was set for Microsoft to submit a final plan on how it would comply with the ruling.

If unhappy with the initial response, the EU would have to send a formal notification to Microsoft, giving the company about 10 working days to respond.

On Tuesday, an EU spokesman said antitrust regulators would probably make a decision on whether or not to hit Microsoft with fines by the end of July.