By Kieran Guilbert

DAKAR, Aug 14 (Thomson Reuters Foundation) - The global outrage sparked by the 2014 kidnapping of more than 200 schoolgirls from Chibok in Nigeria inspired Boko Haram to start strapping suicide bombs to women in a bid to gain notoriety through "shock and awe" tactics, researchers said.

The Islamist jihadists have used more women and girls in bombing attacks than any other insurgency in history — 244 since 2014 — according to a report by researchers at the Combating Terrorism Center at West Point, a leading U.S. military academy.

Boko Haram is also the first militant group to use more female than male bombers, with women accounting for at least 56 percent of 434 suicide attacks carried out during its eight-year campaign to carve out an Islamic caliphate in northeast Nigeria.

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Women and girls are deployed as bombers by Boko Haram — many are forced to do so but some blow themselves up willingly — as they arouse less suspicion and are seen by the militants as more expendable than men, said the "Exploding Stereotypes" report.

But the fact Boko Haram only started using female bombers in 2014 — after the Chibok kidnappings — suggests the group adopted the tactic to grab headlines by "eliciting shock and awe from the local and international community", the report authors said.

"Through the global response to the Chibok abductions, the insurgency learned the potent symbolic value of young female bodies ... that using them as bombers would attract attention and spread pervasive insecurity," said co-author Hilary Matfess.

"I think the media attention and international campaign around the girls motivated Boko Haram ... to enact atrocities on women as a means of building its brand," Matfess told the Thomson Reuters Foundation by phone.

Thousands of women and girls have been kidnapped by Boko Haram, with many being used as cooks, sex slaves and suicide bombers, and others being deployed as fighters, activists say.

The kidnapping of the Chibok girls in April 2014 remains the group's most high-profile attack - provoking an international outcry and a viral celebrity-backed campaign on social media with the hashtag "bringbackourgirls".

The militants have killed more than 20,000 people and forced 2.7 million to flee their homes across Nigeria, Niger, Chad and Cameroon, and show no signs of slowing down despite assertions by the army and state that they are on the verge of defeat.

"One thing that has remained constant about Boko Haram is its relentless innovation - it is a remarkably flexible group," Matfess said. "Expect them to continue to innovate in their suicide bombings tactics, to cause ever more shock and fear."

(Reporting By Kieran Guilbert, Editing by Astrid Zweynert. @azweynert. Please credit the Thomson Reuters Foundation, the charitable arm of Thomson Reuters, that covers humanitarian news, women's rights, trafficking, property rights, climate change and resilience. Visit http://news.trust.org)