Parents and supporters in Nigeria have marked six months since Islamists abducted more than 200 girls from a secondary school.
Nigerian police on Tuesday blocked protesters demanding the release of the schoolgirls from marching on President Goodluck Jonathan's official residence in the capital, Abuja.
On April 14, dozens of fighters from Islamist militant group Boko Haram stormed an undefended secondary school in the remote northeastern village of Chibok, carting away around 270 girls, more than 200 of whom remain in captivity.
Boko Haram leader Abubakar Shekau later threatened to sell the remainder as slave brides, vowing they would not be released until militant prisoners were freed from jail.
Jonathan has been criticized at home and abroad for his slow response to the kidnapping and for the inability of Nigerian troops to quell the violence by the militants, seen as the biggest security threat to Africa's top economy and leading energy producer.