Apple iTunes customers in China fear the online store has been blocked after a pro-Tibet album featured on the site became a hit.
The site has been unavailable inside China for the past week.
An Apple spokeswoman said the firm was currently investigating what lay behind the problem.
The Beijing authorities have not commented on the issue, but activists claim it is connected to the recent release of "Songs for Tibet".
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Popular download
Users of iTunes in China have complained that they have been unable to download music since Monday - a day after the Art of Peace Foundation announced the release of the pro-Tibet album.
BBC staff in Beijing confirmed on Friday that the site was still not working.
The album has been a popular download across the world, and has featured on the front pages of the iTunes stores.
A review page for the album attracted a strong exchange of views between pro-Tibet campaigners and Chinese nationalists.
Michael Wohl, the Art of Peace Foundation's executive, said he believed the album was the reason for the disruption to iTunes, although he had no proof.
Those who contributed to the album include artists Alanis Morissette and Underworld, and there is also a 15-minute talk by the Dalai Lama, the exiled Tibetan leader.
(BBC)
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