EU antitrust regulators fined Microsoft 561 million euros ($731 million) on Wednesday for breaking a promise to offer European consumers a choice of web browser.

Microsoft had made the pledge in 2009 in settling an antitrust investigation in Europe, where the software group's regulatory troubles date from the last decade and have cost it a total of 2.16 billion euros, including the latest fine.

Microsoft promised to offer European consumers a choice of rival browsers in the previous version of its Windows operating system. But the European Commission, which acts as competition regulator across the 27-member European Union, said it found the company broke that undertaking between May 2011 and July 2012.

The Commission said it takes such settlement commitments very seriously.

"Legally binding commitments reached in antitrust decisions play a very important role in our enforcement policy because they allow for rapid solutions to competition problems," Competition Commissioner Joaquin Almunia said in a statement.

"Of course, such decisions require strict compliance. A failure to comply is a very serious infringement that must be sanctioned accordingly," he said. – Reuters