They blamed the paramilitary Rapid Support Forces (RSF) for Monday's attack on al-Luweib village as mourners had gathered in a tent. The RSF has not yet commented.
Many reportedly died before getting to hospital in el-Obeid, a strategic city that connects the capital, Khartoum, to the western region of Darfur.
Fighting has intensified in this oil-rich Kordofan area and around 20,000 people fled to el-Obeid last week after the RSF captured Bara town, 30km (18 miles) north of the city.
The town fell at the same time as the city of el-Fasher, which had been the army's last stronghold in Darfur.
There have since been reports of mass killings, sexual violence, abductions and widespread looting in el-Fasher by RSF fighters.The UN said summary executions of civilians by RSF fighters had also also been reported in Bara.
An attack on a funeral in the key city of El-Obeid in Sudan’s central Kordofan region killed 40 people, the United Nations’ humanitarian office said Wednesday.
The statement did not specify what day the attack took place or who was behind it, but it came as the paramilitary Rapid Support Forces (RSF) had appeared poised to launch an offensive on the city, with army troops also gathering in a a bid to repel them
“The security situation in the Kordofan region continues to worsen,” the Office for the Coordination of Humanitarian Affairs said.