Crowds protested into the night in Sudan against a military coup, with chaos engulfing the capital Khartoum after soldiers opened fire on demonstrators and reportedly killed three people.

Sudan's top general declared a state of emergency and dissolved the government -- one of several similar takeovers in Africa this year -- sparking swift condemnation from the United States, which suspended aid and urged that civilian government be restored.

The United Nations demanded the prime minister's "immediate release" and diplomats in New York told AFP the Security Council was expected to meet to discuss the crisis on Tuesday.

General Abdel Fattah al-Burhan's announcement came after the armed forces detained the civilian leaders who have been heading the transition to full civilian rule following the April 2019 overthrow of autocrat Omar al-Bashir.

"To rectify the revolution's course, we have decided to declare a state of emergency nationwide... dissolve the transitional sovereign council, and dissolve the cabinet," said Burhan.

Clashes erupted in the capital Khartoum after his speech, with the information ministry saying soldiers "fired live bullets on protesters rejecting the military coup outside the army headquarters".

Three protesters were killed and about 80 people wounded, according to the independent Central Committee of Sudan Doctors.

- Internet cut -

"Civilian rule is the people's choice," chanted the demonstrators, who waved flags and used tyres to create burning barricades.

The violence outside the army headquarters came after soldiers detained Prime Minister Abdalla Hamdok, ministers in his government and civilian members of the ruling council, the information ministry said.

Internet services were cut across the country and roads into Khartoum were shut, before soldiers stormed the headquarters of the state broadcaster in the capital's twin city of Omdurman, the ministry said.

The United States, which has been a key supporter of Sudan's transition, said it had suspended $700 million in aid.

"The United States strongly condemns the actions of the Sudanese military forces," said Secretary of State Antony Blinken, calling for the restoration of the civilian-led transitional government. 

State Department spokesman Ned Price said US officials had not been able to contact the detained prime minister.

UN Secretary-General Antonio Guterres said in a statement the detention of the civilian leaders was "unlawful" and condemned "the ongoing military coup d'etat".

The European Union, African Union and Arab League also expressed concern.

- 'Existential moment' -

A 2019 power-sharing deal saw Sudan ruled by a Sovereign Council of civilian and military representatives tasked with overseeing a transition to a full civilian government.

But in recent weeks, the cracks in the leadership had grown wide.

Hamdok had previously described splits in the transitional government as the "worst and most dangerous crisis" facing the transition.

Jonas Horner from the International Crisis Group think tank called it an "existential moment for both sides".

"This kind of intervention... really puts autocracy back on the menu," he said.

Bashir, who ruled Sudan with an iron fist for three decades, is in jail in Khartoum following a corruption conviction.

He is wanted by the International Criminal Court to face charges of genocide over the civil war in Darfur.

But UN High Commissioner for Human Rights Michelle Bachelet warned Sudan risked returning to oppression.

"It would be disastrous if Sudan goes backwards after finally bringing an end to decades of repressive dictatorship," Bachelet said.

- 'Give our lives' -

In recent days, two factions of the movement that spearheaded demonstrations against Bashir have protested on opposite sides of the debate -- one group calling for military rule, the other for a full handover of power.

Tensions  have long simmered within the movement, known as Forces for Freedom and Change (FFC), but divisions ratcheted up after what the government said was a failed coup on September 21 this year.

One FFC leader warned of a "creeping coup" on the weekend at a news conference in Khartoum that was attacked by a mob.

On Monday, the mainstream FFC appealed for nationwide "civil disobedience".

Protesters were seen marching through the streets of Khartoum carrying the Sudanese flag.

"We will not accept military rule, and we are ready to give our lives for the democratic transition in Sudan," said one demonstrator, Haitham Mohamed.

"We will not leave the streets until the civilian government is back," Sawsan Bashir, another protester, told AFP.

Generals determined not to lose long-held power: analysts

By ousting senior civilian figures and disrupting a transition to democracy, Sudan's generals have ensured they maintain control in the East African country, as they have for most of its post-independence history, analysts say.

On Monday security forces detained civilian leaders, including Prime Minister Abdalla Hamdok, who have shared power with the military following the ouster of the autocratic president Field Marshal Omar al-Bashir more than two years ago.

General Abdel Fattah al-Burhan declared a state of emergency and dissolved the cabinet, as well as the ruling Sovereign Council of military and civilian figures which he has led since August 2019.

The Council was supposed to pave the way for full civilian rule.

Since its independence from Britain and Egypt in 1956, Sudan has experienced rare democratic interludes, but overwhelmingly years of rule under military leaders.

The latest putsch "looks very much like an attempt by the security forces to maintain control over economic and political interests, and to resist the flip" to a civilian order, said Jonas Horner of the International Crisis Group.

The army's move "epitomises their fears" of civilian rule "in a country which was under the control of the military for 52 out of its 65 years of independence," Horner said.

To Magdi el-Gizouli of the Rift Valley Institute "the coup was far from surprising". 

The Sovereign Council ruled the country alongside a transitional government led by Hamdok, an economist, but the role of civilian leaders had been receding.

The main civilian bloc, the Forces for Freedom and Change (FFC) which led anti-Bashir protests, splintered into two opposing factions, one of which held demonstrations in support of the military.

- An 'engineered' crisis -

Critics alleged those protests were being driven by members of the military and security forces, and involved counter-revolutionary sympathisers with the former regime.

"The crisis at hand is engineered -- and is in the shape of a creeping coup," mainstream FFC leader Yasser Arman said two days before the military made its move.

Last month the government said it had thwarted a coup attempt, and Burhan dismissed as "slander" suggestions that the army was involved in that manoeuvre.

Ahmed Soliman, an analyst from Britain's Chatham House think-tank, told AFP the military has resisted significant reforms including "professionalisation and civilian oversight" of its institutions, as well as its business interests.

The military dominates lucrative companies specialising in everything from agriculture to infrastructure projects. 

Hamdok said last year that 80 percent of the country's public resources were "outside the finance ministry's control", although he did not specify the proportion controlled by the army.

Such "really critical issues in the transition have fuelled very recent turmoil that is taking place in Sudan and perhaps set the stage for this hostile takeover by the military," Soliman said.

The military's actions are likely to lead to more instability, he added, so "apart from securing their own interests" it is difficult to know what the officers are trying to achieve, Soliman added.

Protests against the coup have already led to three deaths on Monday, and there will be "heavy civilian resistance", Gizouli said.

"The military will have little option but to crush it by force," he said.

Gizouli believes Burhan will remain in power for the foreseeable future but might talk with civilian leaders who remain free, like Foreign Minister Mariam al-Mahdi.

"He still needs a civilian face for the government," Gizouli said.