Intelligence sources believe girls kidnapped from a school in Nigeria may have been split into four groups after they were taken by militant Islamist group Boko Haram, making finding them an increasingly difficult task.
Sources claim British and American officials are using advanced eavesdropping equipment to scan the Sambisa forest where the girls are believed to be, Sky News has reported.
Fifty-three girls have managed to escape Boko Haram's clutches but over 200 remain captive after being abducted from a secondary school in Chibok in remote northeastern Nigeria on 14 April.
The terror group’s leader Abubakar Shekau claimed responsibility for their abductions in a video, where he threatened to sell the girls off as slaves. A further eight school girls were abducted from a Nigerian village by the group this week.
The news comes as Michelle Obama delivered her husband’s weekly presidential address, where she denounced the mass abduction and called for their immediate release.
Ms Obama recently tweeted her support for the ‘bring back our girls’ campaign and expressed “outrage and heartbreak the president and she share over the kidnapping” during the speech ahead of Mother’s Day in America.
Although the First Lady has appeared many times next to the US president as he gives the weekly address, this was the first time she delivered the speech by herself.
"The first lady hopes that the courage of these young girls serves as an inspiration... and a call to action for people around the world to fight to ensure that every girl receives the education that is their birthright", White House deputy spokesman Eric Schultz said.
On Friday, Amnesty International claimed Nigeria’s military was warned of an Islamist attack on the town four hours before the attack took place but failed to act.
The “damning” claim that warnings failed to galvanise the military into preventing the abductions was made as the US-based organisation released details of information from its “multiple interviews with credible sources”.
The Nigerian government dismissed these claims as “unfounded”.
“If the government was aware [beforehand] there would have been an intervention [against the militants],” the Information Minister, Labaran Maku, told BBC World TV. However, he said the government would investigate the claims.
Several countries, including the United States, Britain, France and China, have offered support to Nigeria to help find the girls. British experts including diplomats, aid workers and Ministry of Defence officials arrived in Nigeria on Friday to advise the government on the search.