Michelle Obama and Malala Yousafzai have become the latest high-profile figures to join worldwide calls for the return of almost 300 schoolgirls kidnapped in Nigeria.
The leader of Boko Haram, an Islamic militant group trying to overthrow the government, threatened to “sell” the girls at a market.
The latest horror inflicted by the rebels, who target educational institutions as part of their campaign against anything perceived to be “Western”, triggered a viral social media campaign across the world.
Mrs Obama tweeted: “Our prayers are with the missing Nigerian girls and their families. It's time to #BringBackOurGirls.”
The tweet included a picture of her in the White House holding a placard displaying the hashtag.
Malala, who became a leading global advocate for girls’ education after surviving an assassination attempt by the Taliban, is pictured holding a #BringBackOurGirls sign in the Twitter profile picture of her organisation.
In an interview with CNN she said the kidnapped students were her “sisters”.
Angelina Jolie, Hilary Clinton, and Amy Poehler are among those lending their support to the campaign.
More than 200 children were taken from school in the town of Chibok last month and eight more from another village on Monday.
None of the girls have been found and the Nigerian government’s perceived failure to rescue them has sparked angry protests.
The US, Britain, France and China have sent experts to help the search.
Boko Haram's uprising has claimed the lives of thousands of Muslims and Christians, including more than 1,500 people killed in attacks so far this year.
The group, whose name roughly translates as “Western education is forbidden”, has targeted schools as well as churches, mosques, government buildings and security forces.
Their bloody campaign has highlighted the stark divide between Nigeria’s wealthier and predominantly Christian south and Muslim north.
Additional reporting by AP