Lagos, Nigeria:
Israel on Sunday joined the international effort to trace more than 200 schoolgirls kidnapped by Islamist militants in Nigeria but Washington said US troops would stay out of any rescue mission.
Nigeria's President Goodluck Jonathan spoke to Israeli Prime Minister Benjamin Netanyahu by telephone and accepted an offer for assistance in finding the girls, who were kidnapped by Boko Haram fighters nearly a month ago.
Britain, the United States and France have already sent specialist teams and equipment to help Nigeria's military in the search, which is concentrated in the remote northeast riven by five years of deadly violence.
Jonathan's spokesman Reuben Abati said the president told Netanyahu that "Nigeria would be pleased to have Israel's globally acknowledged anti-terrorism expertise deployed to support its ongoing operations".
French President Francois Hollande, meanwhile, said on a visit to Azerbaijan that a summit on security in west Africa focusing on Boko Haram could be held as early as this Saturday "if the countries agree".
The government in Abuja was criticised as slow to respond to find the girls and Amnesty International claimed on Friday that the military had prior warning about the impending abduction.
But it has been forced into action after a groundswell of national and international outrage that has included protest marches across the world.
US, British and French help involves the deployment of military intelligence and surveillance specialists. China has also offered help.
Washington, however, maintained that its assistance did not extend to troops.
"There's no intention, at this point, to (put) American boots on the ground," Hagel told ABC television, admitting that finding the 223 girls still missing would be no easy task.
Jonathan has said he believes the girls were still in Nigeria and searches were being conducted in the Sambisa forest area of northeastern Borno state, where the military has previously found Boko Haram camps and arms caches.
There have been fears, however, that the girls may have been moved across the border into Chad and Cameroon.
'Utterly merciless'Boko Haram, whose name translates loosely from the Hausa language spoken widely in northern Nigeria as "Western education is sin", has attacked schools, Christian churches, government installations and, increasingly, civilians since 2009.
This year alone more than 1,500 people have been killed, despite a state of emergency imposed in three northeast states in May last year which was designed to put down the insurgency but has failed to stem the bloodshed.
The group was blamed for another attack on Friday night that completely destroyed the village of Liman Kara in northeastern Adamawa state.
Kidnappings of young girls and women has been a previous tactic but the scale of the abduction in Chibok, Borno state, on April 14 and threats from Boko Haram leader Abubakar Shekau to sell the girls as slaves has galvanised the international community into action.
US First Lady Michelle Obama in a recorded message on Saturday said the kidnappings as "unconscionable", adding to condemnation from governments and religious leaders of all faiths to Hollywood celebrities, business figures and people around the world.
The leader of the world's Anglicans, Archbishop of Canterbury Justin Welby warned that dealing with the group would be fraught with danger as his opposite number in the Roman Catholic church, Pope Francis, pledged his support for the girls' return.
Welby, an oil executive before joining the Church, has experience of negotiating with violent groups in the oil-producing Niger Delta region in southern Nigeria.
He told BBC radio in an interview that the girls faced a "colossal" risk.
"They're in the hands of a very disparate group which is extremely irrational and difficult to deal with and utterly merciless in the example it's shown in the past, and it must be a huge concern," he said.
Negotiating would be "extremely complicated" because of Boko Haram's disparate structure, while poverty and mass unemployment in mainly Muslim north Nigeria -- factors seen as fuelling support for the group -- had to be addressed, he added.