In addition to the attack on the cemetery, Emergency Lawyers said that drones struck homes in a residential neighbourhood, the airport district and areas surrounding an army base. Thirteen civilians were killed, the group said, as civilians gathered near destroyed houses.
It also reported that five civilians were killed in earlier attacks.
“It is tragic. The roofs of houses collapsed on their occupants. When you look at some houses, you feel no-one could have survived,” one resident told the AFP news agency in the wake of the attacks.
In another attack a driver of a lorry carrying food supplies died when his vehicle was struck on Thursday, both Emergency Lawyers and Sudan Doctors Network have said.
The two groups describe systematic and repeated attacks on civilians in el-Obeid for several days.
The city is in the country’s oil-rich Kordofan region – which is divided into North, South and West Kordofan states.
It become a major front line in the war due to its strategic significance, sitting between RSF-controlled areas in the west and eastern areas where the army is mostly in charge.
Analysts say whoever controls the region effectively controls the country’s oil supply, as well as a large chunk of the country.