Michelle Obama uses presidential radio address to express outrage at the abduction of at least 200 girls by militant Islamists Boko Haram in Nigeria last month.
The US first lady said: "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.
"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."
Militants stormed a secondary school in the village of Chibok, near the Cameroon border, on April 14, and rounded up the girls, who were taking exams at the time. Fifty have since escaped, but more than 200 remain with the insurgents.
The Nigerian authorities say they believe the girls are still in the country. Mrs Obama added: "I want you to know that Barack has directed our government to do everything possible to support the Nigerian government's efforts to find these girls and bring them home.
"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."
British team arrives
A team of UK experts has arrived in Nigeria to help track down the missing girls, the Foreign Office said.
A spokesman said: "The team is drawn from across government, including the Department for International Development, Foreign and Commonwealth Office and Ministry of Defence, and will work with the Nigerian authorities leading on the abductions and terrorism in Nigeria.
"The team will be considering not just the recent incidents but also longer-term counter-terrorism solutions to prevent such attacks in the future and defeat Boko Haram.
"The team will be working closely with their US counterparts and others to co-ordinate efforts."
The US, China, France and Spain have also promised help.
A report by Amnesty International claims Nigerian commanders were warned that armed men were beginning to arrive near the school but the military were unable to raise enough troops to respond.
Amnesty spokeswoman Susanna Flood said: "This abduction could have been prevented."
The Nigerian government, who have come under growing criticism both at home and abroad for being too slow to react, say they do not believe the Amnesty International allegations are true but they are investigating them.
Demonstrations in support of the missing Nigerian girls have been held around the world and a social media campaign - dubbed #BringBackOurGirls - continues to grow.
Demonstrations in support of the missing Nigerian girls have been held around the world and the social media campaign #BringBackOurGirls has attracted support from celebrities and activists like girls' education campaigner Malala Yousafzai.