The Sudanese military and a powerful paramilitary group battled for control of the chaos-stricken nation for a second day Sunday, signaling they were unwilling to end hostilities despite mounting diplomatic pressure to cease fire.

Heavy fighting involving armored vehicles, truck-mounted machine guns and war planes raged Sunday in the capital of Khartoum, the adjoining city of Omdurman and in flashpoints across the country. The rival forces are believed to have tens of thousands of fighters each in the capital alone.

At least 56 civilians were reported killed, including three employees of the U.N. food agency. The Sudan Doctors' Syndicate said it believed there were dozens of additional deaths among the rival forces. It said close to 600 people were wounded, including civilians and fighters.

The clashes are part of a power struggle between Gen. Abdel-Fattah Burhan, the commander of the armed forces, and Gen. Mohammed Hamdan Dagalo, the head of the Rapid Support Forces group. The two generals are former allies who jointly orchestrated an October 2021 military coup that derailed Sudan's short-lived transition to democracy.

In recent months, internationally backed negotiations revived hopes for an orderly transition to democracy. However, growing tensions between Burhan and Dagalo eventually delayed a deal with political parties.

In Khartoum and Omdurman, fighting was reported around the military headquarters, Khartoum International Airport and state television headquarters. A senior military official said RSF fighters clashed with troops at military headquarters early Sunday and that a fire broke out at a facility for ground troops.

"The battles have not stopped," said prominent rights advocate Tahani Abass who lives near the military headquarters. "They are shooting against each other in the streets. It's an all-out war in residential areas."

Abass said her family spent the night huddling on the ground floor of their home. "No one was able to sleep and the kids were crying and screaming with every explosion," she said. Sounds of gunfire were heard while she was speaking to The Associated Press.

The military and the RSF both claimed to be in control of strategic locations in Khartoum and elsewhere in the county. Their claims couldn't be independently verified.

Both sides signaled late Saturday that they were unwilling to negotiate.