Feb 25 (Reuters) - Mattel Inc had received a subpoena in December from the U.S. Securities and Exchange Commission seeking documents related to a whistleblower letter and subsequent investigation, the U.S. toymaker said in a filing on Tuesday.

In connection with the letter, an independent investigation by Mattel's audit committee and a separate probe by the company's external auditor found that the lead audit partner of the external auditor violated SEC rules. (https://bit.ly/2VyctQ7)

Mattel had disclosed in August that it received the anonymous letter. (Reporting by Sanjana Shivdas in Bengaluru, Editing by Sherry Jacob-Phillips)