She said the world has not forgotten about the girls.
Machel, who is a prominent child rights activist, said to the parents:
“I shook hands with all of you and feel what is in your blood… I share the pain with you of not knowing when the girls will come back,” she reportedly told the parents.
She also urged Nigerian and the international community to do more to free the missing girls.
Seventeen of the girls' parents have died since their abduction, the BBC's Umar Elleman reports from the city.