A team of UK experts has arrived in Nigeria to help with the hunt for 276 kidnapped schoolgirls, the Foreign Office said.
They are in the capital Abuja to help bolster the international effort to find the girls who were kidnapped nearly a month ago, and also to defeat Boko Haram, the Islamic extremists who took them.
The move comes amid international outrage over the mass abduction and a report by Amnesty International which claims Nigerian commanders were warned that armed men were beginning to arrive near Chibok, where the girls were kidnapped from their school, but the military were unable to raise enough troops to respond.
It is more than three weeks since the girls were abducted and Boko Haram has threatened to 'sell' them
A Foreign Office spokesman said: "The team is drawn from across government, including the Department for International Development, Foreign and Commonwealth Office and Ministry of Defence, and will work with the Nigerian authorities leading on the abductions and terrorism in Nigeria.
"The team will be considering not just the recent incidents but also longer-term counter-terrorism solutions to prevent such attacks in the future and defeat Boko Haram.
"The team will be working closely with their US counterparts and others to co-ordinate efforts."
China, France and Spain have also promised help.
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Sky News reported that the search for the schoolgirls is closing in on a forest near the border with Cameroon and that the girls have been divided into at least four groups which would make a rescue raid more difficult.
Nigerian security forces had four hours of notice about the April 15 Chibok attack but did not react because of their fear of engaging the extremists, according to the Amnesty International report citing multiple interviews with credible sources.
A mother of one of the missing Chibok school girls cries during a rally pressing for the release of the girls
Amnesty spokeswoman Susanna Flood said: "This abduction could have been prevented."
The Nigerian government, who have come under growing criticism both at home and abroad for being too slow to react, say they do not believe the Amnesty International allegations are true but they are investigating them.
Speaking to Sky News' special correspondent Alex Crawford, Shettima Haruma, whose daughter was among those taken, said he was "angry" with the Nigerian government's response.
He said: "We beg Nigerians, those in another country like America or (Britain) ... it's three weeks, nearly one month ... (and we haven't) seen any letters from our daughters."
The search for the missing schoolgirls is focused around the huge Sambisa Forest - the "hideout" of Boko Haram, whose name is said to figuratively mean "Western education is forbidden".
In a strongly-worded statement the UN Security Council in New York stressed its "profound outrage" at the kidnapping and condemned it "in the strongest terms".
Demonstrations in support of the missing Nigerian girls have been held around the world and a social media campaign - dubbed #BringBackOurGirls - continues to grow.
Michelle Obama and girls' education campaigner Malala Yousafzai have shown their support.
The US First Lady said Saturday that she and her husband Barack Obama were "outraged and heartbroken" over the abduction.
Actress Emma Watson tweeted: "It's important that these men are held accountable for their crimes and that we keep up the pressure to find these girls. #BringBackOurGirls."