BAMAKO, Mali — Without warning other governments, Algeria mounted an assault on Thursday on the heavily armed fighters holding American and other hostages at a remote Sahara gas field facility, freeing captives and killing kidnappers but leaving some hostages dead and foreign leaders scrambling to find out the fates of their citizens.

Hours after the raid, there was no official word on the number of hostages who had been freed, killed or still held captive. Estimates of the foreign casualties ranged from 4 to 35, though one Algerian official said the high figure was “exaggerated.”

Despite requests for communication and pleas to consider the safety of their abducted citizens, the United States, Britain and Japan said they had not been told in advance about the military assault, stirring frustration that the Algerians might have been overly aggressive and caused needless casualties.

But the Algerian government, which has a history of violent suppression of Islamist militancy, stood by its decision to deal forcefully with the kidnappers, who were holding Algerians and citizens of nine other countries.