No promises over Nigerian girls
Nigerian president-elect Muhammadu Buhari has said he cannot promise to find 219 schoolgirls abducted by Islamic extremists a year ago.
He said their whereabouts are unknown, adding: "We do not know if the Chibok girls can be rescued."
Activists are marking the anniversary of the mass abduction from a school in Chibok, a town in north-east Nigeria, with a change in their slogan from "Bring Back Our Girls - Now and Alive" to "Never to be Forgotten".
Pakistani activist Yousafzai Malala, meanwhile, has promised the girls scholarships and says they must never lose hope.
The 17-year-old Nobel Prize laureate criticised president Goodluck Jonathan and the international community, saying they have not done enough to rescue the girls.
Boko Haram has kidnapped hundreds more since then.
"As much as I wish to, I cannot promise that we can find them," Mr Buhari said in a statement.
The failure to rescue the girls elicited condemnation of Mr Jonathan's government and the Nigerian military, which has repeatedly made false statements about the girls and continues to make hollow promises to bring them home.
Those failures contributed to Mr Jonathan's thrashing at the polls on March 28 by Mr Buhari, a former military dictator who says he is a convert to democracy and has promised a new approach.
"We hear the anguish of our citizens and intend to respond accordingly," his statement said. "This new approach must also begin with honesty."
The kidnapping sparked a mass movement around the world around the hashtag #BringBackOurGirls. In New York City, the campaign said the Empire State Building will be lit up over the hours the girls were snatched, in its purple and red colours symbolising its call for an end to violence against women and girls.
At least 2,000 women and girls have been abducted by Boko Haram since the start of last year, and many have been forced into sexual slavery and trained to fight, Amnesty International said in a report marking the anniversary.
Hundreds of boys and young men have also been kidnapped and forced to fight with the extremists, or slaughtered for refusing to do so, it said.
There has been no confirmation of many reports about the Chibok girls: Boko Haram leader Abubakar Shekau's claim that they had converted to Islam and been married off to his fighters; witness reports that some have been carried across to Cameroon in canoes; reports they were married to fighters in Cameroon; fears that they were among young women and girls turned into suicide bombers by the Islamic extremists; and fears that their bodies are among those of Boko Haram "wives" beheaded as the fighters fled Baga town last month.