By Matthew Mpoke Bigg and Lanre Ola

ABUJA/MAIDUGURI (Reuters) - Nigerian President Goodluck Jonathan promised on Thursday to find more than 200 schoolgirls abducted by Islamist rebels, as the hostage crisis overshadowed his opening address to a conference designed to showcase investment opportunities in Africa's biggest economy.

Speaking at the World Economic Forum (WEF) in the capital Abuja, Jonathan thanked foreign nations including the United States, Britain, France and China for their support in trying to rescue the girls, who were kidnapped from a secondary school on April 14 by Boko Haram.

He also praised delegates for coming despite the danger posed by the militants, then quickly moved on to a speech about creating jobs in African economies.

"As a nation we are facing attack from terrorism," Jonathan told delegates. "I believe that the kidnap of these girls will be the beginning of the end of terrorism in Nigeria."

Despite such promises, Jonathan admitted on national television this week that he had no idea where the girls were.

The kidnappings and numerous other attacks by Boko Haram militants have overshadowed Nigeria's hosting of the forum, an annual gathering of the rich and powerful that replicates the one in Davos, Switzerland.

Security for the event was tight. Police and military trucks blocked off all roads leading to the Abuja Transcorp Hilton hotel, where the event was based. Soldiers patrolled the hotel's grounds and the perimeter with automatic weapons.

Parents of the kidnapped girls said troops had arrived in Chibok on a mission to find the girls.

"There are about three military helicopters hovering around our town and many soldiers have just arrived," said Maina Chibok, who has a 16-year-old daughter with the rebels.

"They are moving and advancing toward the bush. We hope and they succeed in rescuing our daughters."

France became the latest nation to offer help on Wednesday, saying it was boosting intelligence ties with Nigeria and sending security service agents there to tackle Boko Haram, the militant group which claimed the kidnapping.

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In the latest big Islamist attack in Nigeria, 125 people were killed on Monday when gunmen rampaged through a town in the northeast near the Cameroon border.

A senator from Borno state, Ahmed Zannah, put the number killed at 300, although local politicians have sometimes been accused of exaggerating casualty figures for political reasons.

Either way, the scale and ferocity of the massacre in Gamburu again underscored how far Nigerian security forces are from protecting civilians in an increasingly violent region.

WAR CRIMES WARNING

On Tuesday, residents of another village in the remote northeastern area where the schoolgirls were kidnapped, said another eight girls were seized by suspected members of Boko Haram.

Boko Haram leader Abubakar Shekau has threatened to sell the girls abducted on April 14 from a secondary school in Chibok "on the market", prompting a warning from the United Nations that this would make the perpetrators liable for war crimes.

Boko Haram's five-year-old insurgency is aimed at reviving a medieval Islamic caliphate in modern Nigeria, whose 170 million people are split roughly evenly between Christians and Muslims, and it is becoming by far the biggest security threat to Africa's top oil producer.

Al Azhar mosque in Egypt, an influential seat of Sunni Muslim learning, condemned the abductions as being against "the tolerant and noble teachings of Islam" and said it "holds the kidnappers responsible for any abuse or harm that befalls these girls".

Last month's kidnapping occurred on the day a bomb blast, also claimed by Boko Haram, killed 75 people on the outskirts of Abuja, the first attack on the capital in two years. Another bomb nearby killed 19 people last week, prompting a few delegates to cancel their trips to the WEF.

The inability of security forces to protect the girls from being attacked or find them in more than three weeks has sparked national and international outrage and led to protests in Abuja and the commercial capital of Lagos.

Boko Haram has emerged in a region that is one of the world's poorest, with high infant mortality, low literacy and massive youth unemployment that creates easy recruits for radical Islam. Campaigners often call on the government do more to tackle the north's underdevelopment, which contrasts with a relatively prosperous, oil-rich and largely Christian south.

Acknowledging this, Africa's richest man, Aliko Dangote, said he would invest $2.3 billion in sugar and rice production in the north of the country, adding that creating employment was key to ending the insurgency there.

Chinese Premier Li Keqiang gave a speech in which he promised "no strings" support for an African plan to develop a continent-wide high speed rail network, and said China has set aside $2 billion for an African Development Fund.

(Additional reporting by Tim Cocks and Chijioke Ohuocha in Abuja, Sami Aboudi in Dubai and Tom Heneghan in Paris; Writing by Tim Cocks; Editing by Giles Elgood and David Stamp)