Nigerian girls abducted
Women protesting against the brutal abduction of the school girlsAFP

Intelligence sources believe they know where the 276 abducted Nigerian schoolgirls are being held.

British and American officials are using advanced eavesdropping equipment to scan the Sembisa forest where it's believed the schoolgirls are being held.

Sky News reports that the intelligence officers believe they have been split into at least four different groups, and scattered in order to complicate the efforts to locate them.

The news comes midst claims that Nigerian security forces were aware of Boko Haram's planned abduction of the 276 girls, four hours before they were taken from a boarding school in Chibok on April 14.

Amnesty International said verified reports from several credible sources confirm the reports of the government's failure to act promptly.

The Nigerian government has rejected the findings as "unfounded".

It has been reported that some of the girls have already been trafficked to neighbouring Chad and Cameroon.

The kidnapping has provoked global outrage, and a social media campaign has gained momentum with US First Lady Michelle Obama, Malala Yousafzai and several celebrities raising awareness of the kidnapping, with the Twitter hashtag #BringBackOurGirls.

Yousafzai, who survived a shooting by the Taliban, has said the world must not stay silent over the abduction.

She told the BBC: "If we remain silent then this will spread, this will happen more and more and more".

Several NGOs have urged the militants to release the girls and put an end to their reign of terror in Nigeria.

The UK, US, France and China have announced they will send intelligence and hostage negotiation experts to help find the missing girls.

A British team of experts sent to "advise and support" the rescue operation touched down in Abuja earlier on Friday.

The Foreign and Commonwealth Office says Britain's aim is not only to find the girls but to eradicate Boko Haram.