Nigerian soldiers charged with countering the “exceptionally brutal” Boko Haram insurgency are outgunned and fearful, and the Pentagon has been reluctant to share intelligence with the Nigerian military because of its own record of brutality, a senior Pentagon official said Thursday.

The Obama administration has asked for assurances from Nigeria that information shared in the widening search for more than 250 abducted schoolgirls will not be misused, said Alice Friend, the Pentagon’s senior policy official for Africa.

She accused the military of “atrocities” in its campaign against the insurgency and said the Pentagon has difficulty finding “clean” units to which it can offer badly needed help and training. U.S. law bars Pentagon aid to units suspected of human rights abuses.

The search for the girls has become “one of the highest priorities” for Washington, State Department Africa policy specialist Robert Jackson told members of the Senate Foreign Relations Committee.

Boko Haram “has no regard for human life,” Jackson said.

But he and other government officials were clear that until now one of the main obstacles to countering Boko Haram and finding the missing girls has been the Nigerian government itself.

The Nigerian army’s 7th Division, deployed against the insurgency in the country’s north, “has recently shown signs of real fear,” Friend said. “They do not have the capabilities, the training or the equipping that Boko Haram does.”

The Islamic insurgency is increasingly taking on the military in direct fighting, she added, and “is exceptionally brutal and indiscriminate in their attacks.”

As a result, “we are now looking at a military force that is, quite frankly, becoming afraid to even engage,” Friend said.

U.S. defense officials on Thursday provided new details about the daunting nature of the search for the schoolgirls, as well as about the nature of the mobilization by Nigeria’s military to find them.

The officials said that Nigeria has surged forces to the northern region where the girls were taken hostage, including as many as four army battalions plus 1,000 special operations forces and 10 army search teams. Those forces have joined the army’s 7th Division.

Still, the officials said the search involves locating more than 250 girls — who appear to have been divided into smaller groups — in a country with a population of 170 million spread across a region the size of West Virginia.

“This is really difficult for the Nigerian government,” said a U.S. defense official who participated in a briefing for reporters at the Pentagon. The officials spoke on the condition that they not be identified.

The Obama administration sent more than two dozen experts and security personnel to the Nigerian capital, Abuja, this week and is conducting reconnaissance flights over the densely forested area where the militants are believed to have taken the missing girls.

The level of U.S. engagement is a departure after years in which the Nigerian government, a frequent U.S. diplomatic and security partner, had refused U.S. advice about how best to counter the rebels. U.S. help was mostly at arm’s length.

One reason, Friend said, was the record of heavy-handed military assaults conducted by the Nigerian military. The United States has accused Nigeria of nearly indiscriminate attacks against militants and against civilians suspected of helping them.

“We are very, very careful to ensure that we are only providing assistance to those who will not use it in ways that may affect civilians or otherwise violate international human rights standards” when considering whether to share intelligence about militants, Friend said.

Although intelligence available to the Pentagon would not normally be subject to the law barring help to human rights abusers, “we nevertheless are exceedingly cautious when it comes to sharing information with the Nigerians because of their unfortunate record,” she said.

The defense officials said Nigerian units have already engaged in skirmishes with Boko Haram militants, but they stopped short of saying that there was any progress in locating the hostages.

Nigerian President Goodluck Jonathan is seeking a six-month extension of emergency military powers used in the past to justify what human rights monitors have called the extrajudicial killings of thousands of civilians suspected of being Boko Haram members or of supporting the group.

The military state of emergency that Jonathan declared at the start of a broad crackdown on Boko Haram was to expire Thursday.

The defense officials estimated that Boko Haram has about 3,000 followers, including front-line fighters as well as supporters and sympathizers willing to help the group. The group has received support and funding from regional al-Qaeda affiliates including al-Qaeda in the Islamic Maghreb, but the relationship between the two organizations was disrupted by the French intervention in Mali last year, the officials said.

Boko Haram is composed almost exclusively of native Nigerians and has often relied on its ability to blend into villages when pressured by the Nigerian government. It has increasingly focused its attacks on Western targets. “They’ve got the capability to launch more and more lethal attacks than we’ve seen them able to do in the past,” a second defense official said.

Still, U.S. officials said that taking Nigerian schoolgirls hostage marked a significant departure from Boko Haram’s pattern of kidnapping Westerners for ransom, a decision that the group’s leader likely knew would raise Boko Haram’s international profile but could also erode its regional support.

The officials played down the effect that U.S. concerns about sharing intelligence and resources with the Nigerian government would have on the current effort.

“The president has made it clear we’re going to share intelligence,” one official said. “There is a belief and a trust that they will use that information to try to locate the schoolgirls.”