The Central Committee of Sudanese Doctors posted on Twitter on Sunday that at least 56 people, among them civilians, had been killed and 595 wounded.

They said there were many uncounted casualties, including military and paramilitary personnel in the western Darfur region and the northern town of Merowe.

The clashes capped months of heightened tensions between the armed forces and the paramilitary Rapid Support Forces (RSF) group. Those tensions had delayed a deal with political parties to get the country back to its short-lived transition to democracy, which was derailed by an October 2021 military coup.

After a day of heavy fighting, the military ruled out negotiations with the RSF, instead calling for the dismantling of what it called a “rebellious militia.” The tough language signaled that the conflict between the former allies, who jointly orchestrated the 2021 coup, was likely to continue.

The fighting erupted early Saturday. The sound of heavy firing could be heard throughout the day across the neighborhoods in and near the capital, where the military and the RSF had massed tens of thousands of troops since the coup.

Witnesses said fighters from both sides fired from armored vehicles and from machine guns mounted on pick-up trucks in densely populated areas. Some tanks were seen in Khartoum. The military said it launched strikes from planes and drones at RSF positions in and around the capital.

The military said in a statement late Saturday that its troops had seized all RSF bases in Omdurman, while residents reported heavy airstrikes on paramilitary positions in and around the capital continued into the night. Sounds of gunfire and explosions were still heard in several parts of Khartoum, they said.

Those in Khartoum described chaotic scenes. “Fire and explosions are everywhere,” said Amal Mohamed, a doctor in a public hospital in Omdurman. “We haven’t seen such battles in Khartoum before,” said resident Abdel-Hamid Mustafa.

One of the flashpoints was Khartoum International Airport. There was no formal announcement that the airport was closed, but major airlines suspended their flights.

Another plane also appeared to have caught fire. Flight-tracking website FlightRadar24 identified it as a Boeing 737 for SkyUp, a Kyiv, Ukraine-based airline. It did not immediately respond to a request for comment.

The Sudan Doctors’ Syndicate said earlier in the day that two civilians were killed at the Khartoum airport. Another man was shot to death in the state of North Kordofan, it said. The BBC said one of its reporters was stopped by soldiers, taken to the military headquarters and beaten.

The leaders of the armed forces and the RSF traded blame over who started Saturday’s fighting and offered conflicting accounts of who was in control of key installations.

Gen. Abdel Fattah Al-Burhan accused the RSF of entering Khartoum airport and setting fire to some planes. He also said all strategic facilities including the military’s headquarters and the Republican palace, the seat of Sudan’s presidency, are under his forces’ control. He threatened to deploy more troops to Khartoum.

The head of the RSF, Gen. Mohammed Hamdan Dagalo, accused Gen. Al-Burhan of starting the battle by surrounding RSF troops. “This criminal, he forced this battle upon us,” he said.

Dagalo told Al Jazeera that he believed the fighting would be over in “the next few days.”

The RSF alleged that its forces controlled strategic locations in Khartoum and the northern city of Merowe some 350 kilometers northwest of the capital. The military dismissed the claims as “lies.”

The fighting comes after months of escalating tensions between the generals and years of political unrest since the 2021 coup.

The tensions stem from a disagreement over how the RSF, headed by Dagalo, should be integrated into the armed forces and what authority should oversee the process. The merger is a key condition of Sudan’s unsigned transition agreement with political groups.

US Secretary of State Antony Blinken and other top diplomats expressed extreme concern over the outbreak of violence. “We urge all actors to stop the violence immediately and avoid further escalations or troop mobilizations and continue talks to resolve outstanding issues,” Blinken wrote on Twitter.

Secretary-General Antonio Guterres; the European Union’s top diplomat, Josep Borrell; the head of the African Union Commission, Moussa Faki Mahamat; the Arab League chief, Ahmed Aboul Gheit; and Qatar all called for a cease-fire and for both parties to return to negotiations.

Egypt, Saudi Arabia and the United Arab Emirates called on those fighting in Sudan to exercise restraint and work toward a political solution.

Former Prime Minister Abdalla Hamdok, who was ousted in the 2021 coup, warned of a possible regional conflict if the fighting escalates. “Shooting must stop immediately,” he said in a video appeal to both sides posted on his Twitter account.

Cameron Hudson, a senior associate with the Center for Strategic and International Studies think-tank and a former US diplomat, said the fighting could become wider and prolonged, calling on the United States to form a coalition of regional countries to pressure the leaders of the military and RSF to de-escalate.

Volker Perthes, the UN envoy for Sudan, and the Saudi ambassador in Sudan Ali Bin Hassan Jaffar were in contact with Gen. Dagalo and Gen, Al-Burhan to try to end the violence, said a UN official who asked for anonymity to discuss internal deliberations.

Chad announced that it is closing its land borders with Sudan.

The clashes also took place in other areas across the country including the northern province, the conflict-ravaged Darfur region, and the strategic coastal city of Port Sudan on the Red Sea, a military official said, speaking on condition of anonymity because he was not authorized to brief the media.