Update: Twitter has declined to comment, saying "We don't comment on individual accounts for privacy and security reasons."
Update 2: It appears that the suspension may have something to do with Anonymous' recent attack on the Westboro Baptist Church. A tweet from a self-proclaimed @YourAnonNews backup account has posted a screenshot of an email from Twitter, which links the suspension to a tweet that exposed personal information belonging to WBC lawyer and member Shirley Phelps-Roper. While we can't confirm the reason for the suspension, it wouldn't be a surprise if the Westboro Baptist Church intervened; it is well-versed in the law, and as the Southern Poverty Law Center notes, it has made a portion of its income by settling civil lawsuits.
Update: The account has now been reinstated, as noted by The Next Web. A new tweet from the account also reiterated the above claim that it had been suspended for posting information about Phelps-Roper.