The unknown individual contacted at least five government officials, including three foreign ministers, a U.S. governor and a member of Congress, according to a State Department cable.

An impostor pretending to be Secretary of State Marco Rubio contacted foreign ministers, a U.S. governor and a member of Congress by sending them voice and text messages that mimic Rubio’s voice and writing style using artificial intelligence-powered software, according to a senior U.S. official and a State Department cable obtained by The Washington Post.

U.S. authorities do not know who is behind the string of impersonation attempts but they believe the culprit was probably attempting to manipulate powerful government officials “with the goal of gaining access to information or accounts,” according to a cable sent by Rubio’s office to State Department employees.

Using both text messaging and the encrypted messaging app Signal, which the Trump administration uses extensively, the impostor “contacted at least five non-Department individuals, including three foreign ministers, a U.S. governor, and a U.S. member of Congress,” said the cable, dated July 3.

The impersonation campaign began in mid-June when the impostor created a Signal account using the display name “Marco.Rubio@state.gov” to contact unsuspecting foreign and domestic diplomats and politicians, said the cable. The display name is not his real email address.

“The actor left voicemails on Signal for at least two targeted individuals and in one instance, sent a text message inviting the individual to communicate on Signal,” said the cable. It also noted that other State Department personnel were impersonated using email.

When asked about the cable, the State Department responded that it would “carry out a thorough investigation and continue to implement safeguards to prevent this from happening in the future.” Officials declined to discuss the contents of the messages or the names of the diplomats and officials who were targeted.