The Pentagon is trying to determine whether American forces involved in a deadly ambush in Niger this month diverted from their routine patrol to embark on an unapproved mission, military officials said on Friday.

The questions have come up because the American and Nigerien soldiers on the patrol have given conflicting accounts about whether they were simply ambushed or were attacked after trying to chase Islamic insurgents, according to military officials from both countries.

The episode has engulfed the White House in crisis and prompted demands from members of Congress for answers about what the soldiers were doing before the attack on Oct. 4.

In interviews with both the Defense Department and The New York Times, Nigerien military officials said that a lightly armed convoy of about 50 Nigerien and American soldiers gave chase to Islamic insurgents on motorcycles until the men crossed the border into Mali, then returned later to ambush the troops.