The US is also sharing commercial satellite
imagery with the Nigerian government,
It comes after militants released a video of
about 130 girls, saying they could be swapped
for jailed fighters.
Boko Haram seized them from a school in the
northern Borno state on 14 April.
"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," said a senior administration
official, who declined to be named.
A team of about 30 US experts – members of
the FBI and defence and state departments – is
in Nigeria to help with the search.
The BBC's Rajini Vaidyanathan in Washington
says the types of aircraft deployed have not
been revealed, but the US has sophisticated
planes that can listen into a wide range of
mobile phone and telecommunications traffic.
Looking for clues
Other officials, quoted by Reuters, said the US
was also considering deploying unmanned
"drone" aircraft to aid the search.
US state department spokeswoman Jen Psaki
said earlier on Monday that intelligence
experts were closely examining the Boko
Haram video for clues that might help locate
Pogu Bitrus, a leader in the town of Chibok,
from where the girls were seized, said
vegetation in the video resembled that in the
nearby Sambisa forest reserve.
The video showed some 136 girls wearing bulky
hijabs. Militants said they had "converted" to
The girls' families have said that most of those
seized are Christians.
Two girls on the video singled out for
questioning said they were Christians but had
converted to Islam.
Boko Haram leader Abubakar Shekau said the
girls could be exchanged for "our brethren in
"I swear to almighty Allah, you will not see
them again until you release our brothers that
you have captured," he said.