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.

A doctors’ group said that at least 56 civilians were killed and that it believed there were dozens of additional deaths among the rival forces. The Sudan Doctors’ Syndicate said close to 600 people were wounded, including civilians and fighters.