"Our intelligence experts are combing through every detail of the video for clues that might help ongoing efforts to secure the release of the girls," State Department spokeswoman Jen Psaki said.
"We have no reason to question its authenticity," she added after AFP obtained a new video said to be of about 130 of the girls kidnapped last month by the Islamic militant Boko Haram group.
In the video, the group's leader Abubakar Shekau said the girls may be released once Nigeria frees all the Boko Haram prisoners it has in custody.
Psaki stressed however that the Nigerian authorities were "in the lead" during the investigation.
A US team arrived on the ground last week in Nigeria to help growing efforts to find more than 200 girls aged between 16 to 18, snatched from their boarding school in the northeast of the country on April 14.