WASHINGTON — The United States has deployed 80 troops to Chad to augment efforts to find the Nigerian schoolgirls recently taken hostage, the White House announced Wednesday, a significant escalation of Washington’s contribution to a crisis that has created global consternation.

The force, made up largely of Air Force personnel, will conduct surveillance flights and operate drone aircraft but will not participate in ground searches, according to U.S. military officials.

“These personnel will support the operation of intelligence, surveillance and reconnaissance aircraft for missions over northern Nigeria and the surrounding area,” the White House said in a statement formally notifying Congress of the deployment. The unit will remain in Chad “until its support resolving the kidnapping is no longer required.”

This month, the Pentagon dispatched a team of eight experts to the Nigerian capital to help search for the more than 200 schoolgirls captured by Boko Haram, a radical Islamist group that holds sway over remote areas in northern Nigeria. They are working with roughly two dozen U.S. law enforcement and intelligence personnel advising the Nigerian government.

U.S. drones have been searching for the girls since May 11. A Pentagon spokesman said Tuesday that having the new unit in Chad, which borders the northeastern tip of Nigeria, will enable longer surveillance flights.

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