Federal prosecutors expect to unseal an indictment against Castro, 94, in Miami on May 20, based on a 1996 incident in which Cuban jets shot down planes operated by a group of Cuban exiles.

The timing of the potential indictment, which would need to be approved by a grand jury, was not immediately clear, but the official said it sounds imminent.

The United States is preparing to indict former Cuban president Raúl Castro over the 1996 shootdown of two civilian planes operated by the exile group Brothers to the Rescue,…