Lagos, Nigeria (CNN) A British member of parliament launched a protest outside the Nigerian embassy in London to help free kidnapped school girl Leah Sharibu, who friends say is being held by terror group Boko Haram for refusing to renounce her Christian faith.

Liberal Democrat MP Tom Brake is staging a sit-in outside the Nigerian High Commission in central London to put pressure on the Nigerian government, he says.

Sharibu,15, was kidnapped alongside more than 100 schoolgirls in February this year.

Boko Haram freed the other schoolgirls after government negotiations, but Sharibu was kept behind.

"There cannot be a clearer example of someone whose human rights are being ignored than that of Leah who is being detained just because she has maintained her Christian faith," Brake said in an email interview with CNN.