At least 13 people have been killed - eight of them children - after a drone strike on a house in the Sudanese city of el-Obeid, says the Sudan Doctors' Network.
Most of the dead were part of the same family, the medical group added.
Although no group has claimed responsibility, the medics say the paramilitary Rapid Support Forces (RSF) carried out the attack in an area controlled by the army, and which it has been trying to penetrate for months.
As the civil war between Sudan's army and RSF rebels approaches its third year, the scale of suffering has seen it described as the world's worst humanitarian crisis by the UN and aid agencies.
To date, more than 11 million people have been forced from their homes by the violence, and hundreds of thousands of people have been killed. Widespread sexual violence is also being used as a weapon of war.
Both the RSF and the Sudanese Armed Forces are accused of atrocities.
Witnesses say Monday's drone attack on the house in el-Obeid happened in a residential neighbourhood.
The Sudan Doctors' Network says it reflects a dangerous escalation of the policy of indiscriminate killing and systematic bombing of safe residential areas.
The city of el-Obeid remains under army control despite the RSF's advance elsewhere in the wider state of North Kordofan.
Analysts say it is a key target for the RSF because of its strategic location between Sudan's capital city, Khartoum, and the Darfur region where they have established a parallel government and are accused of genocide.
The attack comes days after the RSF hit a power plant in el-Obeid, and also follows what the army claims was an attempted RSF drone attack on the country's largest hydro-electric dam near the northern town of Merowe.
