Victims of the Easter suicide bombings in Sri Lanka last year are still waiting for justice 18 months on, says Open Doors.
The string of attacks on churches and hotels left more than 250 people dead, including scores of children.
Open Doors spokesperson Tala Dela Cruz said the tragedy was "still so heartbreaking" for the Christian community in Sri Lanka.
A year and a half later, some of the injured are still receiving medical treatment.
"These targeted attacks have brought so much pain," he said.
"We are still praying for justice for the victims and healing for their families."
Three luxury hotels and three churches - Zion Church, St Anthony's shrine and St Sebastian's Church - were targeted on Easter Sunday last year.
The Islamic State later claimed responsibility for the attacks.
While investigations are ongoing, Open Doors said several suspects have been released, with the Sri Lankan government blaming lack of evidence.
Earlier this month, relatives of the victims gathered in front of St Sebastian's Church to protest, and call for a fair and thorough investigation.
The Archbishop of Colombo, Cardinal Malcolm Ranjith, has also criticised the failure of the authorities to bring the perpetrators to justice.
He said at a recent press conference: "It is sad and unfortunate that those who are alleged to have been involved in the attacks are released.
"Those who are affected physically and mentally wait for justice to be meted out, but it is unfortunate that the investigation is not going the way it should."