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 on the recovery effort.

U.S. surveillance 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 Tuesday 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, Lt. Col. Myles B. Caggins III.

U.S. military officials have emphasized the difficult nature of the mission. On Tuesday, Rear Adm. John Kirby, the Pentagon press secretary, called the search for the missing girls tantamount to finding “a needle in a jungle.”

“We’re talking about an area roughly the size of West Virginia, and it’s dense forest jungle,” he told reporters.

The Ni­ger­ian girls were abducted in mid-April from a boarding school in the town of Chibok. U.S. officials have said the kidnappers may have broken up the hostages into smaller groups and dispersed into a wider area. Some officials have speculated that the girls could have been smuggled into neighboring countries.

“I don’t think anybody’s underestimating the level of difficulty in both finding them and then being able to launch some kind of recovery mission,” Kirby said Tuesday. “It’s very difficult in terms of the geography, the actual size, just square miles, of what we’re trying to search.”

Officials at the Pentagon would not say precisely where the new unit is based, but the French military has an air base in the Chadian capital, N’Djamena, near the Ni­ger­ian border. Washington and Paris have coordinated closely on security matters in Africa as the threat posed by militant groups there has prompted the United States to significantly expand its military footprint across the continent.

Paul Lubeck, a sociology professor at the University of California at Santa Cruz who has done extensive research in Nigeria, said the country’s security forces are up against a formidable group in Boko Haram.

“These guys are better organized, more highly motivated and have better arms than the Niger­ian military,” he said. “The Nigerian military is decayed.”

Additionally, because the Ni­ger­ian force has a history of brutality, U.S. military advisers face restrictions in the assistance they are able to provide. As part of an agreement reached this week, American military personnel are permitted to share some information — such as aerial imagery — but not all raw intelligence.

As the United States steps up intelligence-gathering efforts there, Lubeck said, there’s the possibility that Nigerian forces could mishandle it.

“Any time the Ni­ger­ian military attempts to intervene to release hostages, the hostages are killed,” he said. “You might get them the intel, but how to get them released safely is the real challenge.”

U.S. Special Operations forces in Africa are engaged in a similarly challenging hunt for Ugandan warlord Joseph Kony, who leads a cult-like group in central Africa that has abducted children to use as sex slaves and soldiers.

The abduction of the Ni­ger­ian girls went largely unnoticed outside Africa for weeks. But as Ni­ger­ians in the capital began protesting the deteriorating security in many parts of the country this month, the plight of the girls began making headlines in the United States and calls for their return gained significant traction on social media.

Several U.S. lawmakers and first lady Michelle Obama have joined the cause, posting photos on Twitter using the hashtag #BringBackOurGirls. Rep. Edward R. Royce (R-Calif.), chairman of the House Foreign Affairs Committee, issued a statement Wednesday calling the deployment a “step in the right direction.” He and others are urging the White House to do more.

“U.S. security personnel should be in Nigeria advising and assisting those engaged in the rescue efforts,” Royce said. “Anything less would be insufficient in responding to the pressing threat that Boko Haram poses to the region and U.S. interests.”