By Slash Lane

Published: 01:00 PM EST

Several users in China have been unable to access iTunes ever since a pro-Tibet album was released on the digital download service earlier this week, prompting an investigation by Apple.

According to the Associated Press, the Art of Peace Foundation announced on Sunday the release of "Songs for Tibet," a digital album comprised of music by popular artists such as Dave Matthews and Alanis Morissette, as well as a 15-minute speech by exiled Tibetan leader Dalai Lama.

One day later, iTunes users began complaining on the official iTunes support forum that they were unable to login and purchase music from the Apple download service. Instead, they were greeted with an error message that said: "iTunes could not connect to the iTunes store. An unknown error occurred.(-4) Make sure your network connection is active and try again."

Others have received a slight variation of that error message. "I am in Shanghai and have been able to use iTunes for 3 years now with no problems, but for the past two days I get an immediate message that the 'network connection was reset,'" wrote a forum poster by the name of jenjen2008.

Although Apple does not operate or support an iTunes Store in China, the company's iPod is widely popular in the region and local customers routinely log into the U.S. or other versions of the store to download media to the devices. While there have been periodic outages from time to time, users on the support forums report that those outages are often resolved quickly. This has lead some to speculate that China may be intentionally blocking iTunes.

Michael Wohl, executive director of the New York-based APF, agrees, telling the AP that he believes the album was the reason for the iTunes interruption, but could not prove it. "We issued a release saying that over 40 (Olympic) athletes downloaded the album in an act of solidarity, and that's what triggered it," he said. "Then everything got blocked."

Apple spokesperson Huang Yuna said the company was aware of the problem but had no comment on the matter for the time being. "We are still investigating," she said.

The AP notes that while Beijing encourages Internet use for education and business, it "tries to block access to foreign sites run by dissidents and human rights and Tibet activists."