U.S. and British experts have arrived in Nigeria to help in the hunt for more than 200 schoolgirls whose abduction last month by Islamists prompted universal outrage.

The U.S. embassy in Abuja told Agence France Presse Friday that a team of American experts had arrived in Nigeria, without specifying the make up of the group.

The insurgency waged by Boko Haram's leader Abubakar Muhammad Shekau, who claimed the kidnapping of more than 200 Nigerian schoolgirls, has grown so ruthless that even former Islamist allies have cut ties.

Born in a village in Nigeria's northeastern Yobe state on the border with Niger, Shekau had a traditional Islamic education in neighboring Borno state, where Boko Haram was founded more than a decade ago by the cleric Mohammed Yusuf.

The Vatican on Thursday appealed for the release of more than 200 schoolgirls kidnapped by the Islamist group Boko Haram in Nigeria, voicing its "compassion" and "horror for the physical and spiritual suffering".

Vatican spokesman Federico Lombardi condemned the "terrorists" and said it was "the latest of the horrible acts of violence that have characterized the activity of this group in Nigeria for a long time".

With international attention focused on Nigeria and the plight of more than 200 girls abducted by Boko Haram, Margee Ensign is keen to stress one thing: it's not just girls at risk from the militants.

"It's children," said Ensign, the president of the American University of Nigeria (AUN), based in Yola, the capital of Adamawa state, which is one of three in northeast Nigeria worst affected by the five-year insurgency.

Nigeria's president said Thursday that Boko Haram's mass abduction of more than 200 schoolgirls would mark a turning point in the battle against the Islamists, as world powers joined the search to rescue the hostages.

President Goodluck Jonathan's administration has struggled to contain Boko Haram's bloody five-year uprising and experts have questioned whether Nigeria can end the violence without help.

World powers, including the United States and China, have joined in the search for the more than 200 schoolgirls abducted by Boko Haram Islamists who have also killed hundreds in the country's northeast this week.

Amid global outrage over the kidnapping of the teenagers, the United States, Britain and France are sending specialist teams to Nigeria.

An attack by Boko Haram Islamists in a northeastern Nigerian town on the Cameroon border has killed hundreds of people, a local senator and witnesses said Wednesday.

Senator Ahmed Zanna added that the town of Gamboru Ngala had been left unguarded because the soldiers based there to protect the population had been redeployed north towards Lake Chad in an effort to rescue more than 200 schoolgirls kidnapped by Boko Haram on April 14.

France on Wednesday offered Nigeria a "special team" to look for more than 200 girls kidnapped by Islamist militant group Boko Haram in an incident that has triggered global shock and condemnation.

The extremists seized a first batch of schoolgirls in Nigeria's restive northeast three weeks ago, saying they were holding them as "slaves" and threatening to sell them, and have since kidnapped other girls in the area.

U.S. President Barack Obama on Tuesday described the kidnapping of more than 220 schoolgirls by Islamists in Nigeria as "heartbreaking" and "outrageous" as Washington deployed military experts in the hunt for the children.

Obama urged global action against Boko Haram and confirmed Nigerian leaders had accepted an offer to deploy US personnel there, soon after residents said the extremist group had seized eight more girls, aged between 12 and 15, again in the embattled northeast.

Suspected Boko Haram Islamists have kidnapped eight more girls from Nigeria's embattled northeast, residents said on Tuesday, after the extremist group's leader claimed responsibility for abducting more than 200 schoolgirls last month.

"They moved door to door looking for girls," said Abdullahi Sani, referring to the late Sunday attack in the village of Warabe, Borno state. "They forcefully took away eight girls between the ages of 12 and 15."