Despite global attention, the actual horror faced by the kidnapped Nigerian schoolgirls has, until now, not yet been known. One of the girls who escaped has revealed how she was raped up to 15 times a day.

A Christian counsellor working with the few who managed to escape their Boko Haram captors reportedly told Nigerian media that this young woman was raped multiple times by different men during her ordeal.

"She found it hard to talk to me but...she confessed to me that she was raped 15 times a day by 15 men throughout the time she was with the Islamic insurgents before she could escape from their den," Oladimeji Thomas told the press.

Despite the shocking nature of this revelation, however, it will unfortunately come as no surprise to those familiar with Boko Haram's activity. The group, formed in 2009, has close ties to Al-Qaeda and is responsible for over 2,000 deaths so far this year alone.

Members of the extremist faction have abducted several groups of women in addition to the estimated 180 who are still missing after being taken from their school in Chibok, Borno state, on the night of April 14.

The abducted schoolgirls are thought to be being held hostage in return for captured militants, though negotiations have so far failed to ensure their release, and Boko Haram leader Abubakar Shekau has declared the girls – many of whom who are Christian – have been "liberated" and converted to Islam.

Fears continue to mount that the girls are being held as sex slaves for militants, as well as forced into domestic servitude.

Former UK prime minister Gordon Brown, who travelled to Nigeria in the wake of the crisis in his capacity as the UN special envoy for global education, earlier condemned Shekau's leadership as "cruel and barbaric".

"It is urgent that all religious leaders in every part of the world speak out against their perverted and twisted version of Islam which involves forced conversions and the sale of girls as sex slaves," he added.