Mustafa Bali of the Syrian Democratic Forces said the victims were refugees from the war the Islamic State (IS) group in the region. He said the attack occurred Saturday near the Conoco gas plant near Deir el-Zour city.
Omar Abu Layla of the activist-run DeirEzzor 24 monitoring group said the blast happened at a checkpoint where locals were awaiting passage into SDF territory. He said dozens were killed.
The SDF control several oil and gas fields in eastern Syria, which they seized from IS militants this year.
A spokesman for US-backed local forces in Syria says more than a hundred people have been killed in a truck bomb blast.