Mexican officials disclosed that four foreigners were present during a counterdrug operation in northern Mexico, not two as previously reported.
The operation, which ended in a crash, resulted in the deaths of two men who were later identified as C.I.A. officers.
The newly released information confirms additional foreign presence at the scene, expanding the initial account of participants involved in the incident.
The details of the operation and the identities of those involved remain under review as officials provide updates on the investigation and its implications.