Release International is one of a number of Christian leaders and organisations urging the US State Department to reinstate Nigeria as a 'Country of Particular Concern' (CPC).
The call reflects increasing desperation over the endless cycle of violence against Christians in the country.
Partners of Release International, which supports persecuted Christians worldwide, estimate that around 17 Christians a day are being murdered in Nigeria - Africa's most populous country.
"Mass killings are now a national emergency," they said.
They argue that returning Nigeria to the State Department's CPC list would increase the international pressure on the country to stop the persecution of Christians.
Release International partners calling on the international community to act include the Anglican Archbishop of Jos, Benjamin Kwashi, the Anglican Church of Nigeria Director of Communications Hassan John, and ChinaAid.
They are among the signatories of an open letter organised by the Family Research Council decrying the decision to remove Nigeria from the list.
The letter speaks of a "slow-motion war" in which more Christians are being killed in Nigeria "than anywhere else on the face of the earth".
"How can it be... that Nigeria's CPC (Country of Particular Concern) designation has been dropped without a public explanation?" they write.
"The ongoing violence, killing, and displacement against Christians and others have only increased. In fact, during 2021, massacres happen almost nightly, while by day, young boys are killed in the fields.
"Pregnant women are brutally dismembered, their babies mutilated before their eyes. And an entire church congregation has been abducted and held captive.
"In recent months, gangs of Fulani militants, Boko Haram terrorists, and other armed radicals have become even more brazen, torching entire villages and farms, ambushing and killing innocent people. The victims are often targeted because of their religious identity.
"Mass killings – the kind that used to be sporadic – are now a national emergency.' They call for 'international pressure... to stop the slow-motion war unfolding in Nigeria ... where more Christians are being killed than anywhere else on the face of the earth."
Release International CEO Paul Robinson said the US State Department appeared to be "ignoring its own warnings".
"Release International has long regarded Nigeria as a country of particular concern. We continue to do so," he said.
"Daily we receive reports of attacks against Christian communities in the north, and those attacks are becoming more widespread.
"The threat is not just from Islamist terror groups like Boko Haram and ISWAP, but also Fulani militants who are attacking far and wide. They appear to be serving the same Islamist agenda of driving the Christian minority out of the north.
"Release urges the international community to insist that Nigeria take effective action to protect its Christians against extremist attacks. The Nigerian government is simply not doing enough. The international community must increase the pressure."
The letter follows the murder of another pastor who was kidnapped for ransom.
Rev Dauda Bature, senior pastor of the Evangelical Church Winning All (ECWA) in Hayin Nariya, Kaduna State, was abducted on 8 November from his farm.
When his wife, Haddasa Bature, attempted to deliver the ransom payment, the kidnappers told her the amount was insufficient and proceeded to abduct her as well, Christian Solidarity Worldwide (CSW) reports.
She was released on 6 December after another ransom payment was made. The kidnappers later claimed to have released Rev Bature, but when the church secretary contacted them two days later, they said he had died a while ago.
CSW's Founder President Mervyn Thomas said: "Our heartfelt prayers and condolences are with Reverend Dauda Bature's family and congregation, and with all those who lost loved ones in the violence in recent days.
"Mrs Bature's ordeal is a grim example of the unimaginable grief, hardship and uncertainty inflicted on families in Kaduna state, at the heart of this crisis of lawlessness.
"We continue to call for a holistic security plan to defeat this threat and to enable civilians to go about their lives in safety.
"These levels of insecurity constitute a national emergency, and we appeal to the Nigerian government to address every source of violence urgently, in order to arrest the country's progressive decline into failed statehood."
