text: In an open letter to the girls, she criticised Nigeria's authorities and the international community for not doing enough to secure their release.
  The Boko Haram militants caused global outrage after abducting the girls from Nigeria's north-eastern Chibok town.
  The UN estimates that the insurgency has now displaced 800,000 children.
  "We cannot imagine the full extent of the horrors you have endured. But please know this: we will never forget you," Ms Yousafzai said in the letter to the 219 girls who were abducted during a night-time raid on their boarding school.
  She added that there were reasons for "hope and optimism", after recent successes by Nigeria's military in regaining territory from Boko Haram.
  "I look forward to the day I can hug each one of you, pray with you, and celebrate your freedom with your families," Ms Yousafzai said.
  In Nigeria, campaign group Bring Back Our Girls has launched a week of events encouraging people to remember the girls ahead of the first anniversary of their abduction on Tuesday.
  A vigil and candlelit procession is due to be held in the capital Abuja.
  The UN children's agency, Unicef, said the abduction of the schoolgirls from Chibok was "only one of the endless tragedies being replicated on an epic scale across Nigeria and the region".
  The number of children fleeing the Boko Haram insurgency has doubled in the past year and more than 1.5 million people have now been displaced in the six-year conflict, Unicef said in a report.
target: Nobel Peace Prize winner Malala Yousafzai has called for more action to free schoolgirls abducted by militant Islamists in Nigeria a year ago.