Nigerian president Goodluck Jonathan has said he believes 200 schoolgirls abducted by Boko Haram last month are still in Nigeria and have not been moved to neighbouring Cameroon.
The abduction has sparked global outrage and Mr Jonathan's government has been criticised for its slow response to the crisis.
Two daughters of Reverend Enock Mark and wife Martha remain missing. Photo: AFP
The president said remote sensors would be used to locate the kidnappers in the Sambisa area, a forest that was a known hideout of the group.
According to a senior American official, the United States is considering a Nigerian request for surveillance aircraft.
British and American advisers are already helping the Nigerians hunt for the girls.
The Nigerian government has denied a claim by Amnesty International that security forces were warned more than four hours in advance about the school attack but did not do enough to stop it.
The president was speaking on the sidelines of the World Economic Forum in the Nigerian capital. The event showcased investment opportunities in Africa's biggest economy but was partially overshadowed by the kidnapping and a broader militant threat.
Mr Jonathan thanked countries including the United States, Britain, France and China for their support in trying to rescue the girls. All have offered assistance and international police agency Interpol on Friday also offered its help.
British experts including diplomats, aid workers and Ministry of Defence officials arrived in Nigeria on Friday to advise the government on the search.
The girls were abducted from a village of Chibok, near the Cameroon border, on 14 April when Boko Haram stormed a secondary school and seized the girls who were taking exams at the time. Fifty have since escaped but more than 200 remain with the insurgents.
The group's struggle for an Islamic state has killed thousands since it erupted in mid-2009 and has destabilised swathes of the northeast of Africa's top oil producer, as well as neighbours Cameroon and Niger.
Nigeria's military has struggled to maintain security in the turbulent northeast as Boko Haram grows bolder.
Comment by grand mufti
Saudi Arabia's grand mufti Sheikh Abdulaziz Al al-Sheikh said Boko Haram had been "misguided" and should be "shown their wrong path and be made to reject it".
His remarks came as religious leaders in the Muslim world, who often do not comment on militant violence, joined in denouncing Boko Haram leader Abubakar Shekau for saying Allah had told him to sell the kidnapped girls as forced brides.
The United Nations Security Council has expressed profound outrage at the abduction, demanding their immediate release and threatening to take action.
