Sudan's military rulers forcefully broke up a weeks-long sit-in outside Khartoum's army headquarters on Monday leaving at least 30 dead and hundreds wounded, doctors close to the protesters said, as gunfire rang out and black smoke shrouded the city.
Heavily armed members of the paramilitary Rapid Support Forces were deployed in large numbers along the capital's main roads.
Manning pick-up trucks mounted with machineguns, they guarded entrances to the bridges that cross the Nile and moved in convoys around the city ahead of evening prayers.
The United States called it a "brutal" crackdown on protesters, who want the generals behind the overthrow of veteran president Omar al-Bashir to hand over to civilian rule.
UN Secretary-General Antonio Guterres condemned the use of excessive force by the security forces against protesters and called for an independent investigation.
The Central Committee of Sudanese Doctors, which is close to the protesters, said the toll "massacre" had "risen to more than 30," with "hundreds of wounded".
An eight-year-old child was among those killed, said the committee.
It reported a "large number of critical casualties" and called for "urgent support" from the International Committee of the Red Cross and other humanitarian organisations to help the wounded.
Beyond the heavy presence of security forces, the streets of the capital were largely empty Monday afternoon, with sporadic cars circulating and a few people walking, because public transport had shut down, an AFP correspondent said.
Many streets remained blocked off by demonstrators who had erected barricades made from stones, tree trunks and burning tyres, although the protesters had departed.
Many shops, pharmacies and businesses were shuttered around the city.
The military council denied its forces violently dispersed the sit-in in front of army headquarters, as demonstrators took to the streets in towns elsewhere in the country.
But protest leaders said the main protest site in Khartoum had been cleared.
"The Rapid Support Forces and the army and police and militia battalions dispersed the peaceful sit-in," said the Alliance for Freedom and Change.
Outside the army headquarters "there is no one, but the pure bodies of our martyrs that it has not been possible to evacuate from the site".
The Sudanese Professionals Association, which spearheaded nationwide protests that started in December, said Monday's crackdown amounted to a "bloody massacre".
It called on Sudanese to take part in "total civil disobedience" to topple the military council.
The doctors' committee said forces had opened fire inside the city's East Nile Hospital and had chased "peaceful protesters".
It said another hospital near the site of the sit-in had been surrounded and that volunteers were prevented from reaching it.
Rallies against Bashir's authoritarian, three-decade rule led to his ouster in April, but protesters had remained outside the army headquarters calling on the generals to cede power to a transitional authority.
Near the demonstration site, a witness living in the Burri neighbourhood said he could "hear the sound of gunfire and I see a plume of smoke rising from the area of the sit-in."
Another resident of the area, in east Khartoum, said he had seen forces in "police uniform" trying to expel the demonstrators.
The military council "did not disperse the sit-in by force," its spokesman said.
"The tents are there, and the youth are moving freely," Shamseddine Kabbashi told Sky News Arabia.
Britain's ambassador to Khartoum, Irfan Siddiq, said he had heard "heavy gunfire" from his residence.
The US embassy in Khartoum said "security forces' attacks against protesters and other civilians is wrong and must stop."
"Responsibility falls on the TMC. The TMC cannot responsibly lead the people of Sudan," it added, referring to the transitional military council.
Tibor Nagy, the assistant secretary of state for African tweeted that it was a "brutal and coordinated attack, led by the Rapid Support Forces militia, that mirrors some of the worst offences of the Bashir regime".
Moussa Faki, the head of the African Union Commission, urged "an immediate and transparent investigation in order to hold all those responsible accountable".
He also called "on the Transitional Military Council to protect the civilians from further harm," a statement said.
Amnesty International urged the international community to consider "all forms of peaceful pressure, including targeted sanctions on those members of the Sudanese transitional authorities responsible for this morning's violent attack on sleeping protesters."
The Alliance for Freedom and Change announced "the end of all political contact and negotiations with the putschist Council" following the deaths, even as neighbouring Egypt appealed for the two sides to talk.
Negotiations between protest leaders and the ruling military council have broken down, as the two sides have failed to agree on whether a planned transitional body would be headed by a civilian or a military figure.