Seven military officials from the US Africa regional command AFRICOM along with a State Department expert arrived Friday, and three FBI personnel and four others from State and the USAID aid agency were due to arrive Saturday.
"They'll be providing technical and investigatory assistance, helping with hostage negotiations, advising on military planning and operations and assisting with intelligence and information," State Department spokeswoman Jen Psaki said.
Among the help on offer would be intelligence-sharing as the teams work to track down the girls seized more than three weeks ago by the Islamic militant Boko Haram group from their school in northeastern Nigeria.
"It's challenging; time is of the essence. It's been, I think, 25 days now since these girls were taken," Psaki told reporters.
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"We're going to do everything possible, but given the circumstances, it's tough and I don't want to make any predictions about the outcome."
Secretary of State John Kerry said in a Twitter chat with young Africans earlier Friday that it was "too early to conclude" the girls would be found.
"Team arriving. Very difficult situation. Determined to do everything we can to help," he added in his Tweet.
Speaking at the World Economic Forum in Nigeria's capital Abuja on Friday, President Goodluck Jonathan restated that his country was "totally committed to getting these girls back."
Nigeria's initial response to the April 14 mass abduction in the northeastern town of Chibok was widely criticized, and for several days Jonathan said very little about the shocking attack.