At least 40 people have been killed in a drone strike on a mourning ceremony near the Sudanese army-held town of El Obeid in Sudan's North Kordofan state, officials and activists say.

They blamed the Sudanese Rapid Response Force (RSF) for the attack on mourners who had gathered in a tent in the village of Al-Luaib on Monday.

Most of the victims of the attack died while being taken to a hospital in El Obeid, a strategically important city that connects Sudan's capital, Khartoum, with Darfur state in the west.

Fighting in the oil-rich Kordofan region has intensified, with some 20,000 residents fleeing to El Obeid.

The residents were displaced a week ago after the rapid response force took control of the town of Bara in the region.

The United Nations has reported that RSF fighters have also committed extrajudicial killings in the city of Bara.

The RSF leader has pledged to investigate the alleged "violations".