At least 65 people, mostly children, have been killed since Saturday in bombardments by the paramilitary Rapid Support Forces in El-Fasher city in Sudan's Darfur region, according to activists.
The capital of North Darfur state is the largest city in the vast western region not yet under the control of the RSF, who have besieged the city since May.
The war between the RSF and Sudan's regular army has been raging since April last year.
The El-Fasher Resistance Committees said in a statement on Monday that "in just three days the RSF have killed more than 43 children, 13 women and nine men among the people of El Fasher".
They added that "more than 70 rockets were launched in just one day by the Janjaweed militias at hospitals, homes, mosques and markets", in a reference to the RSF, who are descendants of the Janjaweed militias which began terrorising Darfur in 2003.
"Today is one of the bloodiest days in El-Fasher, for the civilian population, the mosques and the hospitals, especially the Saudi hospital", the governor of the Darfur region Mini Minawi wrote on social media site X.
A medical source in the Saudi Hospital, which was the target of heavy fire, earlier said artillery shelling killed 22 people on Saturday.
Minawi added that the RSF had received "two days ago a missile system from El-Geneina", the capital of West Darfur.
"The silence of the international community is shameful", he said.
Sudan's war, which pits the RSF, led by Mohamed Hamdan Daglo, against the army headed by General Abdel Fattah al-Burhan, has killed tens of thousands of people with some estimates as high as 150,000, according to United States envoy Tom Perriello.
The United Nations says Sudan faces the world's largest internal displacement crisis, with more than seven million forced to flee internally or abroad because of the war, on top of 3.8 million who were displaced before.
Sudan's conflict has sparked warnings of famine, and both sides have been accused of war crimes including deliberately targeting civilians.
US mediators are to make a new attempt in Switzerland next month to broker an end to the fighting. The talks are due to open on August 14.