The United States is now using drones and manned surveillance 
aircraft over Nigeria in the search for the hundreds of schoolgirls 
kidnapped by Boko Haram.
But signs of them are yet
 to emerge, as the task is complicated by the possibility that the girls
 have been separated into groups.
The U.S., which is 
supporting the Nigerian government's efforts, will continue to deepen 
its efforts, Defense Secretary Chuck Hagel said Wednesday while 
traveling to Saudi Arabia.
However, "I have seen no intelligence come back that I am aware of that shows that we've located those girls," he said
The assets provide some 
of the best tools to try to find the girls, but the Nigerian government 
has shown some reluctance to use U.S. help.
As it is, the U.S. is not sharing raw intelligence from its surveillance aircraft with Nigeria's armed forces.
This is because the 
countries have still not established the intelligence-sharing protocols 
and safeguards needed for an intelligence-sharing agreement, Pentagon 
spokesman Col. Steve Warren said.
That said, the 
intelligence gathered through the surveillance flights is being fed to 
an interdisciplinary team on the ground, and that team is analyzing it 
and providing advice to the Nigerian government, he said.
Warren added that the manned and unmanned aircraft being used are unarmed.
Pressure to find the girls
Wednesday marked one 
month since the 276 girls were abducted from Chibok by Boko Haram. A 
worldwide campaign to "bring back our girls" has spread awareness of the
 incident, and as the days go by, the pressure to find them steps up.
U.S. Sen. John McCain, R-Arizona, is among those who support American military intervention to find the girls, if needed.
"You know, it's 
interesting to me that when a ship is hijacked and taken into custody by
 these pirates, we have ... no reservations about going in and trying to
 take that ship back and the crew that's being held," he said. "We have 
no compunctions about that."
When it comes to the hundreds of girls who were kidnapped, the response has been dragging, he said.
A U.S. military 
operation "could be done in a way that is very efficient, but for us not
 to do that, in my opinion, would be an abrogation of our 
responsibilities," McCain said.
Two senior 
administration officials told CNN that it is premature to talk about a 
special operations incursion into Nigeria because the girls have not 
been found yet.
The U.S. military is there to advise and assist, but not to actively participate, the sources said.
If the girls are found, it would be up to the Nigerians to devise a plan and execute it with U.S. assistance, the sources said.
And that raises other complications.
The Nigerian military is
 capable of carrying out a rescue operation, but there are concerns 
because it has been heavy-handed in the past and killed many civilians, 
the sources said.
As it currently stands, 
U.S. law prohibits the U.S. military from working with Nigerian military
 units that have been accused of abuses, a senior State Department 
official said.
"We've been very clear 
about our concerns about the Nigerian reports of and evidence of abuses 
by the Nigerian military," the official said.
Even with all of these complications, the U.S. is committed to doing everything it can to find the girls, the official said.