At least one of the Chibok schoolgirls abducted by Boko Haram in 2014 has managed to escape captivity, Open Doors reports.
Hauwa Halima Maigana was one of the 276 mostly Christian girls to have been abducted by the terrorist group from their school in Nigeria seven years ago.
Open Doors said it was possible other girls had managed to escape but sources on the ground could not confirm numbers.
"One of the Chibok girls who has escaped was able to speak to her father over the phone and has been clearly identified," said Illia Djadi, Open Doors senior analyst on freedom of religion and belief in sub-Saharan Africa.
Henrietta Blyth, the CEO of Open Doors UK and Ireland, said: "The news of girls escaping from Boko Haram – including the schoolgirl from Chibok – is a ray of hope that others still in captivity may regain their freedom too.
"The abduction of the Chibok girls seven years ago was a painful illustration of the fact that women are especially vulnerable to persecution in Nigeria because of both their faith and gender.
"Even after escape, their painful journey is normally not yet over - they need to reintegrate into their community and cope with the trauma of their captivity."
Over the years, some of the Chibok schoolgirls have been released or managed to escape but at least a hundred remain in captivity.
Djadi said it had been "seven years of anxiety and terrible agony" for their parents, and warned that the problem of abductions had not ended with Chibok.
"In the northeast of Nigeria, Boko Haram spreads terror with its systematic raids on predominantly Christian communities with abductions, sexual violence, and roadblock killings," he continued.
"Christians have been specifically targeted and disproportionately been affected by this violence."
According to data from Open Doors, 990 Christians were abducted by Islamist militant groups in Nigeria in 2020.
Djadi criticised the Nigerian government for failing to keep Christians safe.
"The responses by the government are clearly not enough, since perpetrators of such violence are able to continue attacking Christians, and other Nigerians, with impunity," he said.
"Over Christmas, a number of predominantly Christian communities including Chibok were left vulnerable to attacks, destructions and killings.
"At Open Doors, we want to reiterate our call to the Nigerian government to make security its main priority and to provide protection for vulnerable communities.
"Without security people living in northern Nigeria, if not in the rest of the country, will not be able to carry out a normal life."