Sudan's warring factions agreed to a 72-hour ceasefire starting on Tuesday, while Western, Arab and Asian nations raced to extract their citizens from the country.

The Sudan Armed Forces (SAF) said the US and Saudi Arabia mediated the truce. US Secretary of State Anthony Blinken announced the agreement first and said it followed two days of intense negotiations. The two sides have not abided by several previous temporary truce deals.

Fighting erupted between the SAF and Rapid Support Forces (RSF) paramilitary group on April 15 and has killed at least 427 people, knocked out hospitals and other services and turned residential areas into war zones.

"During this period, the United States urges the SAF and RSF to immediately and fully uphold the ceasefire," Blinken said in a statement.

He said the US would coordinate with regional, international and Sudanese civilian interests to create a committee that would oversee work on a permanent ceasefire and humanitarian arrangements.

The RSF confirmed in Khartoum that it had agreed to the ceasefire, starting at midnight, to facilitate humanitarian efforts. "We affirm our commitment to a complete ceasefire during the truce period", the RSF said.

The SAF said on its Facebook page that it also agreed to the truce deal. A coalition of Sudanese civil society groups that had been part of negotiations on a transition to democracy welcomed the news.

Ahead of the evening truce announcement, air strikes and ground fighting shook Omdurman, one of three adjacent cities in the capital region, and there were also clashes in capital Khartoum, a Reuters reporter said.

Dark smoke enveloped the sky near the international airport in central Khartoum, adjacent to army headquarters, and booms of artillery fire rattled the surroundings.

UN Secretary-General Antonio Guterres said that the violence in a country that flanks the Red Sea, Horn of Africa and Sahel regions "risks a catastrophic conflagration... that could engulf the whole region and beyond".

The Security Council has planned a meeting on Sudan on Tuesday.

Thousands flee

Tens of thousands of people, including Sudanese and citizens from neighbouring countries, have fled in the past few days to Egypt, Chad and South Sudan, despite the instability and difficult living conditions there.

Foreign governments have been working to bring their nationals to safety. One 65-vehicle convoy took dozens of children, along with hundreds of diplomats and aid workers, on an 800km, 35-hour journey in searing heat from Khartoum to Port Sudan on the Red Sea.

For those remaining in Africa's third-largest country, where a third of its 46 million people needed aid even before the violence, the situation was increasingly bleak.

There were acute shortages of food, clean water, medicines and fuel and limited communications and electricity, with prices skyrocketing, said deputy UN  spokesperson Farhan Haq.

He cited reports of looting of humanitarian supplies and said "intense fighting" in Khartoum as well as in Northern, Blue Nile, North Kordofan and Darfur states was hindering relief operations.

Facing attacks, aid organisations were among those withdrawing staff, and the World Food Programme suspended its food distribution mission, one of the largest in the world.

"The quick evacuation of Westerners means that the country is on the brink of collapse. But we expect a greater role from them in supporting stability by pressuring the two sides to stop the war," said Suleiman Awad, a 43-year-old academician in Omdurman.

Several nations, including Canada, France, Poland, Switzerland and the United States, have halted embassy operations until further notice.

The fighting calmed enough over the weekend for the United States and Britain to get embassy staff out, triggering a rush of evacuations of hundreds of foreign nationals by countries ranging from Gulf Arab states to Russia, Japan and South Korea.

Japan said all its citizens who wished to leave Sudan had been evacuated. Paris said it had arranged evacuations of 491 people, including 196 French citizens and others from 36 other nationalities. A French warship was heading for Port Sudan to pick up more evacuees.

Four German air force planes evacuated more than 400 people of various nationalities from Sudan as of Monday, while the Saudi Foreign Ministry said on Monday it evacuated 356 people, including 101 Saudis and people of 26 other nationalities.

Several countries sent military planes from Djibouti. Families with children crowded into Spanish and French military transport aircraft, while a group of nuns were among the evacuees on an Italian plane, photographs showed.

The UN secretary-general urged the 15 members of the Security Council to use their clout to return Sudan to the path of democratic transition.

Islamist autocrat Omar al-Bashir was overthrown in a popular uprising in 2019, and the army and RSF jointly mounted a 2021 military coup. But two years later, they fell out during negotiations to integrate and form a civilian government.

- Reuters