Los Angeles Unified School District Superintendent Albert Carvalho on Saturday condemned racist text messages being sent to Black Americans across the country and said some of the messages were sent to students in the district.

We are aware of racist and incendiary texts that are being sent nationwide, including to some of our students, Carvalho said in a message Saturday afternoon. We unequivocally condemn this hateful and threatening rhetoric. We are investigating this situation. If you receive one of these messages, students and families should contact their school for support.

The source of the messages is unclear. Reports began surfacing Wednesday of messages in several states, making references to slavery and picking cotton.

The FBI is investigating the reports.

The FBI is aware of the offensive and racist text messages sent to individuals around the country and is in contact with the Justice Department and other federal authorities on the matter, the agency said in a statement.