HOUSTON (AP) — Texas is set to execute its first inmate with a new batch of drugs this week. But the state prison system is determined to keep its supplier secret.

The Texas Department of Criminal Justice obtained a new supply of pentobarbital two weeks ago. Since then, it has refused to disclose details, citing threats to pharmacies that sell drugs used in lethal injections.

On Tuesday, the agency revealed some details in a brief filed with the state attorney general's office. It says an individual had threatened to blow up a truck outside a pharmacy supplying execution substances.

The agency says the threat shows Texas shouldn't have to grant an open-records request filed by a death-row inmate's attorney seeking the drugmaker's name.

Similar requests, and refusals, have arisen in several other states.