Nigeria's president for weeks refused international help to search for more than 300 girls abducted from a school by Islamic extremists, one in a series of missteps that have led to growing international outrage against the government.

The British Foreign Office says the United Kingdom offered help the day after the mass abduction. And the U.S. has said its embassy and staff agencies offered help "from day one" of the crisis, according to Secretary of State John Kerry.

'The major challenge remains the fact that some of the information given here turned out in many occasions to be misleading ... Nevertheless, this will not discourage the collaborative efforts that are on-going.'- General Chris Olukolade

Yet it was only this week that Nigeria accepted help from the U.S., Britain, France and China.

The delay underlines an apparent lack of urgency from the government and military to find the girls, for reasons that include a reluctance to bring in outsiders as well as possible infiltration by the extremists.

The government of President Goodluck Jonathan has faced criticism for its slow response since Boko Haram militants stormed a secondary school in the village of Chibok, near the Cameroon border, on April 14, and kidnapped the girls, who were taking exams. Fifty have escaped but more than 200 remain with the insurgents.

The waiting has left parents in agony, especially since they fear some of their daughters have been forced into marriage with their abductors for a nominal bride price of $12. Boko Haram leader Abubakar Shekau called the girls slaves in a video this week and vowed to sell them.

"For a good 11 days, our daughters were sitting in one place," said Enoch Mark, the anguished father of two girls abducted from the Chibok Government Girls Secondary School. "They camped them near Chibok, not more than 30 kilometres, and no help in hand. For a good 11 days."

'Collaborative efforts'

Meanwhile, Nigeria's Army has now posted two divisions to hunt for 200 schoolgirls abducted last month by Boko Haram — an attack condemned globally including by U.S. first lady Michelle Obama on Saturday.

The soldiers are stationed in the border region close to Chad, Cameroon and Niger to work with other security agencies, said General Chris Olukolade, spokesman for the Defence Headquarters.

"The facilities of the Nigerian Army signals as well as all the communication facilities of the Nigerian Police and all the services have been devoted into coordinating this search," Olukolade said in a statement.

"The major challenge remains the fact that some of the information given here turned out in many occasions to be misleading .... Nevertheless, this will not discourage the collaborative efforts that are on-going," he said.

The air force has flown more than 250 sorties, a signals unit and the police are involved and a multinational task force has also been activated and surveillance equipment is deployed in support of ten search teams, he said.

The United States, Britain, France, China and international police agency Interpol have all offered assistance.

Pope Francis also tweeted on Saturday to his four million followers using the hashtag #BringBackOurGirls.

Jonathan on Friday said he believed the schoolgirls remained in Nigeria and had not been transported into Cameroon. It was the first indication he has given of their whereabouts.

The attackers were based in the Sambisa area of Borno state, a Boko Haram stronghold near the school from where the girls were abducted, he said.

Boko Haram's fight for an Islamic state has killed thousands since it erupted in mid-2009 and has destabilized swathes of the northeast of Nigeria, Africa's top oil producer, as well as neighbours Cameroon and Niger.

The global outrage over the attack has shone a spotlight on the rebellion and institutional challenges faced by the government and military just as Nigeria's economy has overtaken South Africa's as the biggest on the continent.

Earlier this month, Boko Haram leader Abubakar Shekau threatened to sell the girls "in the market".

The kidnappings and a broader militant threat overshadowed the World Economic Forum held in the Nigerian capital this week that showcased investment and opportunity in the country of 160 million people.

Human rights group Amnesty International said in a statement, citing multiple interviews with sources, that the security forces had been warned more than four hours in advance of the school attack but did not do enough to stop it. Olukolade dismissed the report as baseless.

With files from Reuters