Nigeria will get more military and tactical support to help combat the Islamist militant group Boko Haram and find 200 kidnapped schoolgirls, African and Western officials pledged at a meeting in London on Thursday.

Although Boko Haram has been fighting for five years, carrying out bombings and attacks on civilians and the security forces, the kidnapping in April of more than 200 girls has focused world attention on them and prompted demands for action.

Ministers from Nigeria and neighbouring Chad, Benin, Niger and Cameroon agreed on Thursday to form a regional intelligence unit to fight Boko Haram, aided by Britain, France and the United States, British Foreign Secretary William Hague said.

They also agreed to run multi-national patrols along the porous borders to stop the group, which is seen as a regional threat. The international community will enhance training for Nigeria's military and provide more schooling for Nigerian children.

"Defeating Boko Haram will be a long and difficult task, but the atrocities against innocent and vulnerable communities are too important to ignore," Hague told reporters on the sidelines of a London summit on ending sexual violence in conflict.

"All of the countries gathered here today have shown that we are certainly not going to ignore them and our resolve to defeat them has been further increased."

The meeting on Thursday followed a similar gathering of West African leaders in Paris in May to try to improve cooperation in the fight against Boko Haram, which is seen as a kind of regional al-Qaeda based in Africa's most populous country.

Boko Haram has killed more than 3,000 people in a five-year campaign to establish an Islamic state in mostly Muslim northeast Nigeria. The outrage over the kidnapping of the schoolgirls has prompted greater international involvement.

Nigerian President Goodluck Jonathan, criticised at home for his government's slow response to the disappearance of the girls from a secondary school, had accepted U.S., British and French intelligence help in the hunt for the youngsters.

But even before the girls were abducted, the rising violence, coupled with a bout of inter-communal killing in Nigeria's fragile middle belt, led many Nigerians to question the long-term viability of Nigeria as a state.

Hague said he would not give running commentary on the search for the schoolgirls, to which Britain sent a surveillance aircraft, but indicated little progress.

"It is clearly formidable terrain and formidable circumstances in which to locate them," he said.

Hague said further meetings would be held to ensure greater cooperation in a bid to combat Boko Haram.

"The defeat of Boko Haram and equipping of regional countries to bring about that defeat will take time," he said.