Is Kraken allowed in the USA?

Could you please clarify if Kraken, the cryptocurrency exchange platform, is legally permitted to operate within the United States of America? Are there any restrictions or regulations that Kraken must adhere to in order to maintain its operations in the country? Additionally, are there any specific states within the USA where Kraken's services may be prohibited or limited? It would be greatly appreciated if you could provide a concise and accurate answer to this question.