The United States has deployed 80 troops to Chad to augment efforts to find the Nigerian schoolgirls recently taken hostage.
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 US 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 sent a team of eight experts to Nigeria to help search for the more than 200 schoolgirls captured by Boko Haram, a radical Islamist group that holds sway over remote areas in the north.
They are working with roughly two dozen US law enforcement and intelligence personnel advising the Nigerian government on the recovery effort.
US drones have been searching for the girls since May 11. Although officials have not said where those drones have been flying from, a Pentagon spokesman said that having the new unit in Chad, which borders the northeastern tip of Nigeria, will enable longer surveillance flights.
"Locating this force in Chad allows us to spend more time flying over the search area," said the spokesman, Lieutenant Colonel Myles Caggins.
US military officials have emphasised the difficult nature of the mission. On Tuesday, Rear Admiral John Kirby, the Pentagon press secretary, compared the search for the missing girls to finding "a needle in a jungle".
The Nigerian girls were abducted in mid-April from a boarding school in the town of Chibok. US officials have said the kidnappers may have broken up the hostages into smaller groups and dispersed into a wider area. Some believe the girls could have been smuggled into neighbouring countries.
Officials at the Pentagon would not say precisely where the new unit is based, but the French military has an air base in the Chad capital, N'Djamena, near the Nigerian border.
The US and French governments have co-ordinated closely on security matters in Africa as the threat posed by militant groups there has prompted the US to significantly expand its military presence.