The outbreak of violence follows years of ratcheting tensions between the Rapid Support Forces (RSF), a major paramilitary group led by Vice President Mohamed Hamdan Dagalo — universally referred to as Hemedti — and the military, headed by Gen. Abdel-Fattah Burhan, the nation’s president.

Shooting broke out around 9 a.m., residents said, and fighting quickly escalated as artillery, armored vehicles and then fighter jets were deployed. Bridges were blocked and three planes at the international airport were hit, witnesses said.

The RSF claimed it had taken control of sites including the presidential palace, Khartoum International Airport, and the airport in Merowe, north of the capital. The Sudanese Armed Forces dismissed RSF statements as “lies.” Both sides blamed the other for attacking first.

In an interview with Al Jazeera, Hemedti described Burhan as “a criminal and a liar who will destroy Sudan,” and pledged to “hand him and his associates over to face justice.” He said 100 military officers and thousands of soldiers had defected to him, without providing evidence.

Burhan, during his al Jazeera interview, said the RSF attacked the seat of the Sovereignty Council and his home that morning and had harassed members of the army in an area south of the capital. He also said the RSF had broken into the Khartoum Airport and set fire to some aircraft, but that the army had repulsed them and remained in control of the army’s general command center, key military facilities and the Republican Palace, without providing evidence.

The Sudanese air force is conducting operations against RSF positions, the military said, sharing unverified footage of military aircraft in the sky and adding “we are waging a battle of national dignity that has long been coming.”

Tensions have run high for months between Sudan’s army and the RSF, which have been sharing power but disagree on how this should be split, and when paramilitary forces should be dissolved as part of a transition to civilian rule.

The violence dates back to the time of former president Omar al-Bashir, who ruled for 30 years and has been wanted by the International Criminal Court for war crimes, crimes against humanity and genocide. He had tried to stave off growing opposition to his rule by encouraging the growth of the Rapid Support Force, a militia that grew out of the Janjaweed in the western region of Darfur. The Janjaweed were blamed for rapes, burning villages and mass killings.

A spiraling cycle of civilian protests and bloody crackdowns toppled Bashir in 2019, ushering in a brief euphoria before the military and RSF seized power in 2021. Diplomatically isolated and economically crippled, the two sides agreed late last year to turn over power over to a civilian-led government. But the deal left key problems unresolved, said Kholood Khair, the founding director of Khartoum-based think tank Confluence Advisory.

“The framework agreement codified the tensions between them,” he said. “It promoted Hemedti from Burhan’s deputy to his equal … It’s made it difficult for Burhan to back this deal. His forces put inordinate pressure on him not to back the final deal, which was due April 1.”

The alliance was always uneasy, she said, noting “They have different foreign policies, allies and income streams and different visions on how to consolidate the coup they led together in 2021.”

The fighting has wider regional implications: Hemedti has been publicly linked to Russia’s Wagner group, while General Burhan has support from neighboring Egypt.

Even if the fighting stops in Khartoum, Khair said, it might continue elsewhere in the country.

“Sudan is on the precipice of civil war,” warned Alan Boswell, director for the Horn of Africa for the International Crisis Group. “This is the double-headed monster that seized power after Bashir. Now the two heads have turned on each other.

On Saturday, fighting was reported in several cities. The U.S. ambassador to Sudan, John Godfrey, said he was sheltering in place with the embassy team after waking up to “gunfire and fighting.” He called on senior military leaders to stop the fighting.

U.S. Secretary of State Antony Blinken tweeted “We urge all actors to stop the violence immediately and avoid further escalations or troop mobilizations and continue talks.”

Cameron Hudson, a senior associate at the Center for Strategic and International Studies, said he had confirmed fighting in the cities of Merowe, Khartoum, el Obeid and the towns of al Fashir and Nyala in Darfur.

“I very seriously take the announcement made by the RSF that they are going after every military base in the country,” he said. “This is a fight to the finish.”

Both sides see the other as an existential threat, he said, and the international community had little leverage since it had already isolated Sudan, whose battered economy desperately needs debt relief.

“Neither Burhan or Hemedti is answering their phones,” he said, noting that regional countries like Saudi Arabia or the United Arab Emirates might take the lead.

It’s not even clear if Burhan fully controls the army, he said, since there’s significant hard line Islamist elements still within it from Bashir’s time. Although both sides had been building up forces for weeks, the fact that phone and internet services were still working and that it took hours to get military planes into the air meant the fighting could have been triggered by a miscalculation, he said.

Witnesses, who asked not to be named for safety reasons, reported seeing armored vehicles and plumes of smoke rising in Khartoum on Saturday morning. Mothers dashed to get their children from school, some unable to return home due to gunfire, armed men blocked bridges and people tried to go home under gunfire, said an activist, citing eyewitness reports from their network.

“There are armored personnel carriers and troops deploying,” said another witness. “I can hear heavy weapons in the distance.”

One of the damaged planes belonged to the United Nations, footage showed, while another belonged to Saudi Arabia’s national airline. It was hit by gunfire as it prepared to depart to Riyadh with guests and crew onboard, the airline said.

Two civilians had been killed at the airport and dozens of injuries reported, the Preliminary Committee of the Sudan Doctors’ Trade Union wrote on Twitter, also calling for the protection of medical personnel, civilians and the injured.

The Radical Change Forces’ Alliance — a pro-democracy coalition of civil society groups — called on people to shelter in their homes. “We hold army leaders and the Janjaweed forces accountable,” the alliance said in a statement posted to Facebook Saturday. “We call on all revolutionary forces to form a broad and cohesive front against war and the merchants of war.”

Sudanese political activist Amgad Fareid, a former assistant chief of staff to the prime minister in the short-lived civilian administration, said the international community had wanted a deal at any cost, he said, and had conveyed legitimacy on Hemedti and Burhan and then pressurized civilians to join the process. Mediators had also buckled in to too many demands, he said, including a long lead time for security sector reform — which strengthened the RSF’s hand — and that the two leaders should could report in parallel to the head of state.

“They were too blind to see who Hemedti and Burhan really are,” he said.

The violence was heartbreaking after so many Sudanese had died for democracy, he said, noting more than 200 had been killed in protests since the coup and many hundreds before it.

“After all the sacrifices the Sudanese people have made, we are sad, disappointed and afraid for the future of this country.”

Francis reported from London and Parker reported from Washington.