U.S. officials 'hitting the ground' in Nigeria to help find missing girls

Nigerian security forces had more than four hours of advance warning but failed to act during last month's Boko Haram attack on the school where more than 200 girls were kidnapped, Amnesty International said Friday.

Six U.S. military advisers arrived in Nigeria on Friday to help in the search for girls kidnapped last month by Islamist militants, a U.S. military official told CNN.

The advisers will join a team of U.S. and British officials already in Nigeria, helping find the girls, planning rescue efforts and devising strategies to help subdue the terror group Boko Haram, which abducted the girls April 14 from a government boarding school.

About 60 U.S. officials have been on the ground since before the kidnappings as part of counterterrorism efforts with Nigeria, a senior U.S. administration official told CNN. They have been holding meetings, getting resources into the country and making assessments with local authorities.

"Our interagency team is hitting the ground in Nigeria now, and they are going to be working ... with President Goodluck Jonathan's government to do everything that we possibly can to return these girls," Secretary of State John Kerry said Thursday.

Their tasks include establishing a coordination cell to provide intelligence, investigations and hostage negotiation expertise.

There are no plans to send American combat troops, according to U.S. Navy Rear Adm. John Kirby, who serves as Pentagon press secretary.

A British team drawn from the country's Department for International Development, the Foreign and Commonwealth Office and the Ministry of Defence also arrived in Abuja on Friday, the foreign office said.

They will work with Nigerian authorities and the U.S. team both on strategies to rescue the girls and on longer-term efforts to defeat Boko Haram, the office said in a statement.

Boko Haram herded nearly 300 girls out of bed under the cover of darkness on April 14 at a school in northeastern Nigeria.

A few escapees shared harrowing tales of escaping into a nearby forest. Authorities said the 276 still missing probably have been separated and taken out of the country.

International outrage has escalated over the nation's largely ineffective effort to subdue Boko Haram.

"By God's grace, we will conquer the terrorists. I believe the kidnap of these girls will be the beginning of the end for terror in Nigeria," Jonathan said at the World Economic Forum meeting in Abuja on Thursday.

In addition to the United States, Jonathan said, Britain, China and France have pledged to help find the girls snatched from the school in Chibok.

The United States' team includes law enforcement experts and military advisers. France also said it is sending a team but didn't provide specifics on what expertise it will bring.

British satellites and advanced tracking capabilities also will be used, and China has promised to provide any intelligence gathered by its satellite network, Nigeria said.

Nigerians protest over kidnapped schoolgirls

"Clearly, there is danger whenever we send troops almost any place in the world," U.S. House Speaker John Boehner said.

"But I do think the President is taking the right step here to work with our allies to try to do everything we can to get these girls back to their families in a safe way."

The task of recovering the girls appeared to grow more complicated with news that U.S. intelligence shows the 276 girls have been split up.

Kirby said they believe the girls "have been broken up into smaller groups" but declined to detail how officials came to the conclusion. His sentiment has been echoed by others.

"The search must be in Niger, Cameroon and Chad, to see if we can find information," said Gordon Brown, a former UK prime minister and the U.N.'s special envoy for global education.

Boko Haram's leader, Abubakar Shekau, took credit for the mass kidnappings in a video that surfaced this week. His group's repulsive violence did not end there.

Suspected Boko Haram militants attacked Gamboru Ngala, a remote state capital near Nigeria's border with Cameroon. The attack Monday targeted an area soldiers use as a staging ground in the search for the girls. Some of the at least 310 victims were burned alive.

"We are also going to do everything possible to counter the menace of Boko Haram," Kerry said. "The entire world should not only be condemning this outrage but should be doing everything possible to help Nigeria in the days ahead."

Nigeria has been accused of failing to take action in the hours and days after the girls were abducted.

"In a hostage situation, time is of the essence," Kirby said. "We lost some time."

Jonathan waited three weeks before speaking to the nation on the matter. He said that rescue efforts were under way at the time but that they could not be disclosed publicly.

CNN's Vladimir Duthiers reported from Abuja, and Faith Karimi reported and wrote from Atlanta. CNN's Elise Labott and Chelsea Carter contributed to this report.