A spokeswoman for Microsoft said the firm was not concerned that Zune player sales had dropped each week since its debut.

'Overall growth'

"While this is expected, our focus is less on week over week numbers, and more on the incremental sales that are leading to overall growth of the category," she said in a statement.

Many analysts see Microsoft's Zune player as a first step in a long-term plan to compete with Apple, reflected in the US-only release of the player.

The 30-gigabyte Zune costs $249 (£130) and comes with wireless technology that allows users to beam photos and songs to one another.

Microsoft has said it plans to invest hundreds of millions of dollars to develop and market the Zune, and has acknowledged that the investment may take years to bear fruit.

The company has taken a similar approach with its Xbox games division, growing sales and credibility in the market while initially having limited success against competitors.