Britain must send air and satellite support to Nigeria to help the search for the missing schoolgirls, former prime minister Gordon Brown has said.
"I've been advocating action for three weeks and it's now time to go beyond the words of comfort," Brown told ITV News.
|We have to extend the search for these girls now beyond Nigeria... into Cameroon, into Chad, into Niger. The air support and surveillance we need and the satellite coverage has now got to go into a number of other states to find the girls."
Brown criticised the international community for its slow response to the kidnapping of almost 300 schoolgirls from their school in Chibok, Borno state, almost a month ago.
"I'm really sorry because three weeks ago I tried to alert the world, I said 'look we need international support to help locate these girls', and I fear they have been dispersed across Africa," Brown said. "We may never hear of them again.
Brown said he had promised the family that "even though it's late, we will do everything in our power to try to locate these girls".
Britain has agreed to send a small team of British experts to Nigeria to offer assistance with planning, co-ordination and advice. The government would not confirm whether the SAS will be among those sent to the region.
Islamist militants from the Boko Haram group have claimed responsibility for the abduction, and a leader warned that he would sell the girls into slavery, raising concerns that they may be moved across the border into neighbouring countries to be forced into work, marriage or prostitution.
Speaking earlier at the World Economic Forum in Nigerian capital Abuja, Brown drew attention to other atrocities committed by Boko Haram, mentioning a separate incident in the past few weeks when seven teachers were murdered and 27 members of their families were abducted in Borno State.
The kidnapping has ignited a viral social media campaign under the hashtag #BringBackOurGirls that has brought renewed attention to Boko Haram's campaign of violence. Yesterday, US first lady Michelle Obama joined in, tweeting, "Our prayers are with the missing Nigerian girls and their families. It's time to #BringBackOurGirls."
Speaking at a film premiere in London this evening, Hollywood star Angelina Jolie said of the social media campaign: "I think it was the people that pushed the governments to step up. It is the power of the people that have made that happen."
Jolie, a UN special envoy, continued: "I pray it's not too late for these girls and I hope they find them and bring them home. I am very concerned but I think it is partially our responsibility for making this culture and community where these men think they can get away with this, because most of the time they do."
A cross-party group of 53 female MPs, including women's ministers Nicky Morgan and Jenny Willott, equalities minister Helen Grant MP and shadow equalities minister Gloria De Piero, issued a statement of support for efforts to reunite the girls with their families.
"The brutal treatment of girls seeking an education - a right we take for granted for our daughters - demonstrates the cruelty and immorality of this group," it said.
Boko Haram's five-year-old Islamic uprising has claimed the lives of thousands of Muslims and Christians, including more than 1,500 people killed in attacks so far this year.
The group, whose name means "Western education is sinful", has tried to root out Western influence by targeting schools, as well as attacking churches, mosques, government buildings and security forces in the country of 170 million, divided between a predominantly Christian south and Muslim north.