Christians gathered in London on Tuesday to protest the ongoing captivity of Nigerian Christian schoolgirl Leah Sharibu. 

The protest outside the Nigerian High Commission coincided with the one-year anniversary of the 15-year-old's abduction by militant group Boko Haram. 

She was taken on February 19, 2018 along with over 100 of her classmates.  While the others were released several weeks later, the group has continued to hold Sharibu over her refusal to deny her Christian faith. 

Last October, a breakaway faction of Boko Haram, the Islamic State West African Province, declared that it would hold Sharibu and another captive, Christian mother-of-two and UNICEF worker Alice Ngaddah, as 'slaves' for life. 

'Based on our doctrines, it is now lawful for us to do whatever we want to do with them,' the group proclaimed.

CSW's Chief Executive Mervyn Thomas said: 'Leah Sharibu has now been in the hands of this violent sect for 365 days and we are deeply concerned by the lack of government action to secure her release.

'We continue to call on the government of Nigeria to do everything in its power to expedite the release of this courageous schoolgirl, alongside that of her fellow hostages.

'We also call on the government of Nigeria to ensure that the army is sufficiently equipped to combat Boko Haram effectively, particularly in light of the surge in activity by both factions, and their threat to undermine the electoral process.'

The protest in London came days after Sharibu's mother, Rebecca, pleaded with the government to take action to free her daughter at a press conference in capital Abuja last week. 

Open Doors' head of advocacy Zoe Smith said: 'Leah Sharibu was kidnapped because she was a girl and held captive because she was a Christian. She personifies the incredibly vulnerable position of Christian women in northern Nigeria.

'It is saddening and outrageous that Leah remains in captivity, abused as a PR tool and negotiating pawn by Boko Haram. We urge the Nigerian government and the international community to increase their efforts to secure her release and reunite her safely with her family.'

Nigeria is number 12 on the 2019 World Watch List, Open Doors' annual ranking of the 50 countries where Christians face the most extreme persecution.