CAIRO (AP) — Heavy artillery fire in a conflict-stricken Sudanese city killed at least 11 people and injured 90 others, aid group Doctors Without Borders said.

In a post Friday on X, formerly known as Twitter, the aid group — known by its French initials MSF — said the attack took place in the Karari neighborhood of Omdurman city Thursday but did not say which of the country’s warring parties were responsible. Children were among the dead, it said.

Sudan has been rocked by violence since mid-April, when tensions between the country’s military, led by Gen. Abdel Fattah Burhan, and the paramilitary Rapid Support Forces, commanded by Gen. Mohamed Hamden Dagalo, burst into open fighting.

The fighting has since spread to several parts of the country, reducing the capital, Khartoum, and neighboring Omdurman to an urban battlefield. The conflict also fueled ethnic violence in Sudan’s western Darfur region.

MSF said those injured in Thursday’s attack were treated at Al Nao hospital in Omdurman, one of several medical facilities where the medical group is operating.

Neither the military nor the Rapid Support Forces immediately responded to a request for comment.

“In September, our teams have already responded to seven mass casualty incidents in hospitals we support. The suffering this brutal fighting is causing for the population is unbearable,” MSF said on X.

The fighting has driven 5.5 million people from their homes in search of safety and refuge, according to the United Nations′ latest figures, with 4.3 million internally displaced within Sudan and 1.2 million crossing into neighboring countries.

At a news conference Thursday, Clementine Nkweta-Salami, the U.N.'s humanitarian coordinator in Sudan, said 18 million people are in need of humanitarian assistance. So far U.N., aid agencies have only reached around 3.6 million people in the country, she said.

“The population of Sudan is balancing on a knife’s edge,” said Nkweta-Salami, describing the situation as “the world’s fastest growing displacement crisis.”

The conflict has killed at least 5,000 and injured more than 12,000 others, according to the United Nations. Activists and doctors groups in the country say the true death is far higher.