Theranos CEO Elizabeth Holmes. WSJ Theranos, the controversial blood-testing startup, is facing a criminal investigation into whether it misled investors about its technology.

The company, which has come under scrutiny following reports about irregularities with its tests, is the subject of a criminal probe by the US attorney's office, as well as a civil probe from the SEC, according to a memo the company sent to its partners on Monday.

Walgreens, which had a partnership to offer the Theranos tests to its customers, and the New York State Department of Health have received subpoenas in recent weeks, seeking documents and other information about the representations that Theranos made, according to a report in The Wall Street Journal.

"In the past, we have generally not commented on the specifics of these inquiries out of deference to our regulators and in light of specific requests for confidentiality. However in light of consistent press attention in this area we want you to hear about them from us," reads Theranos' memo, which was obtained by Business Insider.

Theranos initially came under fire after an October 2015 article in The Journal questioned the accuracy of its tests, which the company had initially said could be done using only a single drop of blood. The privately held company was valued at $9 billion in a 2014 funding round, according to The Journal.

In an emailed statement to Business Insider, a Theranos representative said that "the company continues to work closely with regulators and is cooperating fully with all investigations."

The Theranos memo notes that separate investigations by the FDA and the Departments of Health in Arizona and Pennsylvania have been "successfully closed out."

The Journal said that federal investigators are also looking at whether Theranos misled government officials, which could be a federal crime. The investigation is at an early stage and the subpoenas do not mean that prosecutors are seeking an indictment, the report noted.

Here's a copy of the memo that Theranos sent to its partners on Monday: