She said she and her husband Barack Obama were “outraged and heartbroken” over the abduction on 14 April of more than 200 girls from their school.
She was speaking instead of her husband in the weekly presidential address.
The Islamist militant group Boko Haram has claimed the abductions
Mrs Obama, who was speaking ahead of Mother’s Day in the US on Sunday, said the girls reminded her and her husband of their own daughters.
“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.