Michelle Obama has taken the unique step of delivering her husband's weekly presidential address to express outrage at the recent kidnapping of Nigerian schoolgirls.

Speaking for the first time instead of the U.S. president, before what is Mothers' Day in the U.S. on Sunday, she said the couple were "outraged and heartbroken" over the abduction of more than 200 girls from a school in the Nigerian town of Chibok on April 14.

"What happened in Nigeria was not an isolated incident. It's a story we see every day as girls around the world risk their lives to pursue their ambitions," she said. "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."