"We are focused on working with the Nigerian government to locate and bring home those girls. That includes a team of individuals. It also includes manned reconnaissance flights that I can confirm we are conducting in cooperation with the Nigerian government," White House Press Secretary Jay Carney told reporters at his daily news conference.
"When it comes to the approach to Boko Haram in this case, Nigeria of course has the lead, and we play a supporting role. It is the policy of the United States to deny kidnappers the benefits of their criminal acts, and that includes ransoms or concessions," Carney said when asked if US President would support negotiations with Boko Haram if they would lead to the release of these young girls.
"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 senior US official said.
Though the types of aircraft deployed have not been released, the US has sophisticated planes that can listen into a wide range of mobile phone and telecommunications traffic.
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A team of about 30 US experts - members of the FBI and defence and state departments - is already in Nigeria to help with the search.
State department spokeswoman Jen Psaki said the US was "providing intelligence, surveillance and reconnaissance support".
Military and law-enforcement teams on the ground were "digging in on the search and co-ordinating closely with the Nigerian government as well as international partners and allies", she said.
More than 270 girls were snatched by militants from their boarding school in Chibok, north-eastern Nigeria, on April 14. Some managed to escape, but most were taken into the remote Sambisa forest.