Twitter declined comment, but noted that its policies forbid violent threats, hate speech or harassment, adding that it will take action against repeat offenders.
Richard Spencer, head of the National Policy Institute, a white nationalist think tank, says his personal Twitter account, as well as the accounts for the institute and his magazine, were all suspended this week without notification.
The Twitter accounts of alt-right personalities Paul Town, Pax Dickinson, Ricky Vaughn and John Rivers also were suspended.
Spencer, who is credited with popularizing the term "alt-right," says he didn't tweet anything recently that might provoke a suspension. He calls the suspensions a coordinated attack against users with certain viewpoints.