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"We have shared commercial satellite imagery with the Nigerians and are flying manned ISR (intelligence, surveillance and reconnaissance) assets over Nigeria with the government's permission," the official said.
The United States has sent military, law-enforcement and development experts to Nigeria to help search for the missing girls who were kidnapped by Boko Haram militants from a secondary school in Chibok in remote northeastern Nigeria on April 14.
"We are providing intelligence, surveillance and reconnaissance support," State Department spokeswoman Jen Psaki told a news briefing. She said US teams on the ground "are digging in on the search and coordinating closely with the Nigerian government as well as international partners and allies."
Last week, US Undersecretary for Africa Linda Thomas-Greenfield told Reuters in an interview that Nigeria had requested surveillance and intelligence from the United States. .
Nigerian President Goodluck Jonathan has said he believes the girls are still in Nigeria. The leader of Boko Haram has offered to release them in exchange for members of its group being detained, according to a video posted on YouTube on Monday.