In the face of ongoing upheaval in Sudan, Release International says there is a "window of opportunity" to end persecution against the country's Christian minority.
The country faces huge uncertainty after a coup last Thursday ousted Omar al Bashir after nearly 30 years in power.
The takeover has concerned Sudan's neighbours, with the African Union threatening to revoke its membership in the organisation unless there is a return to civilian rule in two weeks.
The AU "strongly condemns and totally rejects the seizure of power by the Sudanese military and its plan to lead the transition for two years," the organisation said in a statement.
Release International, which supports the persecuted church worldwide, said that the unrest may be an opportunity to end years of oppression against Christians.
Persecution has been especially severe in the Nuba Mountains region, where Release said the Sudanese government was engaging in "ethnic cleansing".
The government has tightened restrictions on religious freedom in recent years, favouring an increasingly strict application of Sharia law in which Muslims who convert to Christianity risk prosecution and death.
Across the country, the authorities have stopped the growth of Christianity by refusing Christians permission to build new churches, while existing church property has in some cases been seized or demolished. Some church leaders have also faced arrest.
With military chief General Abdel Fattah al-Burhan releasing hundreds of political prisoners, Release CEO Paul Robinson said the upheaval could also open the door to greater religious freedom.
"This could be a turning point where all that could change," he said.
"These are encouraging steps. But the next step must be to allow full religious freedom in the country. Without true freedom of belief and association, Sudan will continue to be one of the most repressive states in the world today.
"Handled well, this could be a window of opportunity for Christians in Sudan, who have suffered immensely for many years."
He said it was time for "change" in the country as he called on the new leaders to implement full religious freedom and join the "free, democratic nations of the world".
"Right now, the world is watching and hoping. This is an opportunity for change and we call on Christians everywhere who enjoy freedom of worship to pray for our brothers and sisters in Sudan," he said.