The United States has deployed surveillance aircraft over a remote area of Nigeria as part of a mounting international effort to find over 200 school girls abducted by the dreaded Boko Haram Islamist militants nearly a month ago.
“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,” a senior US official said on Monday.
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.
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.
The plight of the schoolgirls and the desperation of their families has captured world attention, with abhorrence focused on Boko Haram, the violent jihadist group that is holding the girls.
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.
Boko Haram on Monday released a 27-minute video, showing about 130 girls in Muslim dress and reading from the Quran. Most of the seized girls are Christians. Two were singled out to tell the camera they had converted to Islam.
In the video, the Boko Haram leader, Abubakar Shekau, said the girls could be released in exchange for jailed militants. "I swear to almighty Allah, you will not see them again until you release our brothers that you have captured," he said.
A US official said they have no reason to question the authenticity of the video.
High-profile figures around the world have backed the campaign for the girls' release.
US First Lady Michelle Obama took over her husband's weekly presidential address to express "outrage and heartbreak" over the mass abduction, and to pledge US government support for the rescue effort.
Apart from the US assistance, Britain, France and China have sent teams to Nigeria to help the search, and Israel has offered to join the international effort.
Boko Haram, whose name means "Western education is forbidden", had previously said the girls should not have been at school and should get married instead. The militants have been engaged in a violent campaign against the Nigerian government since 2009.
Image: Boko Haram released a video of the girls they claimed to have abducted