Christian groups are pleading with the Nigerian government to do more to protect civilians from abductions and free those already in captivity.
The call has been issued after reports of at least 600 people, including women and children, being kidnapped in Nigeria last week alone.
Many of the kidnapping victims were living in camps for internally displaced persons in the northern state of Borno.
In a separate incident, at least 287 students and teachers were kidnapped by armed herders from a school in Kuriga, Kaduna State.
The timing is particularly sensitive as next month will mark the 10th anniversary of the kidnapping of 276 girls from their school in Chibok by the Boko Haram terrorist group. While some were released and others escaped, around 100 remain in captivity a decade on.
Jabez Musa, a Nigerian lawyer and partner of Open Doors whose real name has been changed for security reasons, says there has been a rise in kidnappings in the country.
"Abductions have been taking place one here another there, but this is quite different now. Our government has not reacted yet. We are waiting to hear from them to see what they can do," he said.
Open Doors said these were "not isolated incidents" as it accused the Nigerian government of "failing to discharge its duty to protect its citizens from violence and attacks".
"Attacks and kidnappings – particularly in the north of Nigeria – have seriously worsened over the last decade. Christians are among those who are especially targeted," a spokesperson said, adding, "Arms proliferation, impunity and government inaction has allowed the expansion of Boko Haram and increasing violence in the north of Nigeria, where attacks by armed bandits on villages and schools are becoming endemic."
CEO of Open Doors UK and Ireland, Henrietta Blyth, has issued an urgent appeal to the Nigerian president to free the victims.
"Boko Haram is notorious for targeting Christians, abducting and killing men and abducting, raping and forcibly marrying women and girls," she said.
"We also urge the Nigerian government to work to get the hostages already held by Boko Haram liberated - including young Christian girls such as Leah Sharibu and the Chibok girls who are still held captive."
Christian Solidarity Worldwide (CSW) said over 50,000 Christians have been killed in Nigeria due to religious persecution over the last 15 years, amounting to a Christian dying every two hours on average.
It said it was "deeply concerned" by the resurgence in mass abductions by terrorist organisations in the country.
CSW's founder president Mervyn Thomas called for the "swift and safe return" of students and for more to be done to protect children from kidnappings.
"It is deeply disturbing that, once again, children simply seeking an education are being treated as commodities to be seized en masse and bartered," he said.
He continued, "For over a decade terrorist groups, including a militia comprising assailants primarily of Fulani ethnicity, have been able to conduct violent attacks and abductions for ransom across Nigeria on an almost daily basis while eliciting a wholly inadequate response from the authorities.
"We therefore urge the current federal administration to become far more proactive in addressing Nigeria's critical security situation by sufficiently resourcing and mandating the armed forces to tackle every insurgency, to liberate all who remain in terrorist captivity, and most crucially, to ensure protection for schools and vulnerable communities."
