A suspected cyber attack has taken Al Qaeda's web discussion forums offline for the longest period since they were set up eight years ago.
The forum Shumukh al-Islam, which has been known as a main source of videos and other material for the group's members and supporters, has been offline since 22 March.
The site's admins reportedly assure their users that the forums will be back up "soon" - but so far it remains inaccessible.
Several other websites were reported to be down by the Washington Post.
It is not known whether the outages are the result of a technical failure or - as some experts suspect - a sustained attack by either a government or a hacking collective such as Anonymous.
According to the Post, American counterrorism agents says they were not involved - and sources quoted by the newspaper note that several prominent Al Qaeda websites remain online.
But NBC News reported another expert who said that the forum's collapse is more likely the result of a technical fault.
British government hackers have previously taken down Al Qaeda websites and corrupted terrorist training manuals.
Officials are also said to rely on the clandestine sites for information about possible attacks, and experts have said it would not be in their interest to take them down.