Mrs Obama said what had to be said

The First Lady has presented the weekly presidential address from the White House, in an unusual break from tradition.

Mrs Obama used the radio and live-streamed statement to call for the release of the 276 Nigerian girls who were abducted by Islamist militant group Boko Haram.

"Like millions of people across the globe, my husband and I are outraged and heartbroken over the kidnapping of more than 200 Nigerian girls from their school dormitory in the middle of the night," she said.

"This unconscionable act was committed by a terrorist group determined to keep these girls from getting an education – grown men attempting to snuff out the aspirations of young girls."

She continued: "In these girls, Barack and I see our own daughters. We see their hopes, their dreams – and we can only imagine the anguish their parents are feeling right now.

"Many of them may have been hesitant to send their daughters off to school, fearing that harm might come their way.

"But they took that risk because they believed in their daughters’ promise and wanted to give them every opportunity to succeed."

Mrs Obama added that students in America should look at the Nigeria situation, and realise that they could not take their own educational opportunities for granted.

"These girls embody the best hope for the future of our world…and we are committed to standing up for them not just in times of tragedy or crisis, but for the long haul."

Mrs Obama has accompanied her husband for the presidential address before, but it is the first time that she has given the speech alone.

And although it is an unusual move, it is not unprecedented – Laura Bush, wife of George W. Bush, was the first to do so in 2001, and took the opportunity to denounce the treatment of women in Afghanistan.

Following the kidnapping of 276 girls on April 14, a campaign to secure their return has mushroomed. Activists are urging the Nigerian government to do more, and claim that President Goodluck Jonathan has been slow to respond and uninterested in their fate.

Mrs Obama last week posted a photo of herself holding up a sign reading "#Bring Back Our Girls" to show her support for the campaign.

On Friday night the United Nations Security Council unanimously declared that the mass kidnappings "may amount to crimes against humanity" under international law. But they made no explicit reference to charges in the International Criminal Court.

The 15 members of the council said they would follow the situation and consider "appropriate measures" to take against Boko Haram.

The statement urged their immediate release, without conditions.

Meanwhile, UN Secretary General Ban Ki-moon announced he was sending his special representative for West Africa, Said Djinnit, to Abuja to discuss ways of helping authorities locate the girls.