A host of Hollywood men, including Sean Penn, Ashton Kutcher, Justin Timberlake and Bradley Cooper, add their voices to the campaign to free the girls

As well as the 284 girls held from the attack on 14 April, Boko Harem has also abducted a further eight girls, aged between eight and 15, in an overnight raid on a village on Monday.

This brings the total held captive to 284, with a further 50 girls managing to escape as the armed rebels made their way through villages away from the school in Chibok, killing people and burning down buildings en-route.

As the days go by with no sign of their daughters, the girls' family members are becoming increasingly fraught.

"They’d assured us they would rescue our children but... we still haven't seen our daughters," one of the victim's mothers, Rahila Bitrus, told Channel 4. "We are going through the very worst moment of our lives."

"There is no way to describe what we are feeling. It is just one long nightmare," one woman whose daughter and niece were abducted told the Guardian.

Michelle Obama urges release of kidnapped schoolgirls in Nigeria, as UK sends assistance