At least 40 people were killed in an airstrike on a market in southern Khartoum, the local volunteer emergency room said in a statement on Sunday.

According to Reuters, it is the largest single-incident civilian death toll of the civil war in Sudan that began on April 15, as fighting in residential areas intensifies.

In mid-April, tensions between the country’s military, led by Gen. Abdel Fattah Burhan, and the Rapid Support Forces, commanded by Gen. Mohamed Hamdan Dagalo, burst into open fighting.

The conflict has killed more than 4,000 people, according to August figures from the United Nations. However, the real toll is almost certainly much higher, doctors and activists say.