The leader of an ill-fated team of American soldiers in Niger last fall warned before the mission that his troops did not have the equipment or intelligence necessary to carry out a kill-or-capture raid against a local militant, according to preliminary findings of a continuing Defense Department investigation.

In a departure from normal lines of authority, the report concludes, the Oct. 4 mission was not approved by senior military officials up the chain of command in West Africa and Germany. Instead, it was ordered by a junior officer, according to two Defense Department officials. Four American soldiers and five Nigeriens were killed when the unit was ambushed.

The two officials said Defense Secretary Jim Mattis and Gen. Joseph F. Dunford Jr., the Joint Chiefs of Staff chairman, are troubled that low-level officers are being blamed for the botched mission instead of senior commanders who should be aware when American troops are undertaking a high-risk raid.