Theranos, the embattled blood-testing laboratory, said on Monday that federal officials were conducting a criminal investigation into the company, adding to a series of questions from officials about its inner workings.

In a note to outside partners, the company said that the Justice Department had requested documents and that the investigation was active. The note also said that the Securities and Exchange Commission was investigating the company.

The note detailed a growing list of inquiries from federal and state officials, many of which have looked into the company’s claims about its technology. The United States attorney’s office in San Francisco, which Theranos said was conducting an investigation, declined to comment, as did the S.E.C. Theranos would not elaborate about the exact nature of its investigation.

The company said the investigations began after The Wall Street Journal published articles about Theranos.