WASHINGTON. Al-Qaeda's main internet forums have been offline for the past 12 days in the longest sustained outages of the sites since they began operating.

No one has claimed responsibility for disabling the sites but the breadth and duration of the outages have prompted speculation the forums have been taken down in a cyber attack - launched perhaps by a government or hacking group.

The first website, Shumukh al-Islam, a primary source for al-Qaeda videos and messages, went down on March 22, and since then four others have gone dark. The administrator of a second-tier al-Qaeda site recently posted a message on an online forum saying that ''the media arena is witnessing a vicious attack by the cross and its helpers on the jihadi media castles''.