Are claims required in a provisional application?

No. Caution, however.  A select number of foreign countries (e.g., China/SIPO) have strict rules prohibiting the Applicant from adding claims. In these countries, adding practically anything will be considered "new matter" -- you cannot merely point to one or more paragraphs in the specification as support for claims you are later trying to add. Therefore, in many cases it is safer to just include a full claim set in a provisional application, even if these claims are not legally required by the United States Patent and Trademark Office. Usually, at the point in time when you file a provisional application, there has been limited or zero market testing on the product. At that phase, it is usually too early to recognize which countries you will eventually be selling your product in. Therefore, in order to keep your options open, the safer play is to include a full claim set in your provisional patent application.  

As a secondary advantage, the process of claim drafting will often cause the patent prosecutor to have a firmer idea of what the invention actually is, and to recognize additional details that should also be included in the specification.