The information comes from the rebel group Sudan Liberation Movement/Army (SLM), which controls the mountainous area of Jebel Marra in Darfur where the affected village of Tarasin is located.
After several days of rain, the landslide occurred on August 31.
"Preliminary information indicates that all villagers, estimated to be more than a thousand individuals, have perished, with only one survivor," it says in a statement from the SLM.
The movement appeals for help from the UN and other aid organizations to recover the dead who are buried under earth and debris.
"The UN and our humanitarian partner organizations are organizing support for the affected residents," writes the UN's humanitarian coordinator Luca Renda in a statement on Tuesday.
But the difficult situation in Sudan, and especially in the vulnerable Darfur province, makes it hard to reach with support efforts.
Sudan is embroiled in a civil war between the army and the paramilitary Rapid Support Forces (RSF), which has plunged the country into one of the world's worst humanitarian crises.
In war-torn Darfur, the fighting has escalated since the army regained control of the capital Khartum in March. Famine prevails in parts of the region, and the situation in Sudan is often described as the world's largest humanitarian crisis.
The SLM has largely remained neutral during the civil war, but parts of the rebel group have recently joined the army's fight to combat the RSF.
