Darfur's strongest rebel group clashed with Sudanese government forces guarding a convoy, sparking a gunfight that killed 57 officers and insurgents, police said.
The fighting in South Darfur state late on Thursday is the latest in a surge of violence in the remote territory since the suspension of peace talks between Khartoum and the rebel Justice and Equality Movement (JEM) last week.
Sudanese police accused JEM of attacking a commercial convoy between the town of Al Deain and the capital of south Darfur Nyala, saying officers guarding the vehicles fought off the assault.
A total of 27 members of Sudan's Central Reserve Police and 30 JEM fighters died in the fighting, police spokesman Mohamed Abdul Majid said in a statement. He added that 87 people from both sides were wounded.
JEM told Reuters its troops came across Sudanese army forces guarding a convoy of military vehicles and ammunition trucks and said the soldiers had fired the first shots.
"A convoy of 165 vehicles of SAF (Sudan Armed Forces) were trying to attack some of our redeployed mobile units in the south of Darfur. We met them. It was a very fierce battle. Those 165 military vehicles and all the forces have been completely rounded up," senior JEM official Al-Tahir al-Feki said.
JEM is one of two rebel forces that took up arms against Sudan's government in 2003, accusing it of marginalising the region's population and starving it of funding.
President Omar Hassan al-Bashir, who mobilised militias to crush the uprising, is facing International Criminal Court charges of masterminding war crimes in the region.
Sudanese authorities have accused JEM of attacking and looting villages across Darfur in recent weeks.
JEM denied the accusations and said it was sending out mobile "administrative" units across Darfur and the neighbouring oil-producing region of South Kordofan to reach out to local leaders and maintain links with outposts.
"When Sudan forces attack us we have to respond," Feki said.
He also denied reports from international sources, who asked not to be named, that JEM forces had destroyed mobile phone masts, cutting off communications along a corridor from their stronghold in West Darfur, southeast towards South Kordofan.
JEM signed a ceasefire and initial peace deal with Khartoum during talks brokered by the government of neighbouring Chad in February. Chad's President Idriss Deby shares ethnic links with JEM's leadership.
Further talks quickly stalled when JEM objected to Khartoum's decision to start separate discussions with another rebel grouping, and the insurgents last week said they were suspending talks in protest against government bombing raids on their bases.