US intelligence believes that the approximately 276 Nigerian school girls abducted last month by Boko Haram terrorists have now been split up and likely taken out of the country.

"We do think they have been broken up into smaller groups," U.S. Navy Rear Adm. John Kirby, the Pentagon press secretary, said.

He declined to detail how U.S. officials came to the conclusion. It is a sentiment that has been echoed by a number of others, who believe the girls already have been moved out of Nigeria and into neighboring countries.

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

"It's vital to use the information to find the girls before they are dispersed across Africa, which is a very real possibility."

The girls have not been seen since Boko Haram militants abducted them on April 14 from the Government Girls Secondary School in rural Chibok, about 80 miles (130 kilometers) west of Maiduguri and some 600 miles from the capital of Abuja.

That was followed on Sunday night by another kidnapping, with villagers in Warabe accusing Boko Haram militants of taking at least eight girls between the ages of 12 and 15.

Boko Haram's leader, Abubakar Shekau, took credit in a video that surfaced this week for the mass kidnappings.

"I abducted your girls," he taunted in the video, first obtained by Agence France Presse. "There is a market for selling humans. Allah says I should sell. He commands me to sell."

Shehu Sani, a former negotiator between Boko Haram and the government, believes the group targeted the girls to force concessions from the Nigerian government -- beginning perhaps with the release of its followers from prisons.

Would a prisoner swap work? One Nigerian who has negotiated with Boko Haram before thinks its the only way to save the girls. Shehu Sani doesn't think the Nigerian government is capable - or serious - about getting the girls back:

The peace negotiator, who has previously traveled to Maiduguri in Borno State, in northeastern Nigeria, for direct talks with Boko Haram leadership in a burned-out mosque, is concerned that international attention is forcing Nigeria’s government to take a hardline but miscalculated approach.

"This government is helpless and hopeless on solving the problem” he said. “The most important thing is to get them back alive, and you cannot do that through force.”

Instead of convening a negotiating mission, the Nigerian government has appointed a committee led by military and intelligence chiefs, to whom Boko Haram will be unwilling to talk, Sani said.

He cited recent examples of armed raids, attempting to rescue foreign hostages, that have resulted in the death of captives.

“The government of Nigeria is pretending to be serious simply because the world is taking an interest,” he said.

Meanwhile, experts from the US and Great Britain arrived on Friday in Nigeria to help with the search:

A Foreign Office statement said the British experts would be working closely with their US counterparts.

"The team will be considering not just the recent incidents but also longer-term counter-terrorism solutions to prevent such attacks in the future and defeat Boko Haram," it said.

Earlier, US Secretary of State John Kerry said: "Our inter-agency team is hitting the ground in Nigeria now and they are going to be working in concert with President Goodluck Jonathan's government to do everything that we possibly can to return these girls to their families and their communities."

"We are also going to do everything possible to counter the menace of Boko Haram," he said.

On Wednesday, President Barack Obama said the team comprised personnel from military, law enforcement and other agencies.

He said he hoped the kidnapping would galvanise the international community to take action against Boko Haram.

Does this sound like the US is helping with a rescue mission? Or working to prevent a similar incident from happening again while working with the Nigerian government to apply pressure to Boko Haram?

Even if the girls are alive, if they're spread out over three countries it is doubtful that they can all be recovered. No doubt, if there was an attack on one site where the girls were held, they would be massacred at other sites. Are there enough military assets to attack all the sites at the same time? Even if all the sites where the girls were held were discovered, it would take military precision and lots of luck to get them all back - something the Nigerian military has failed to demonstrate in their war against Boko Haram.

You don't want to give up hope. Perhaps a negotiated settlement can be reached. But the longer the girls are held, the less likely it is they will be returned alive to their loved ones.