Volker Perthes told an emergency meeting of the UN Security Council the two warring parties remain convinced that "securing a military victory over the other is possible" and that neither is "ready to seriously negotiate."

"This is a miscalculation," said Perthes, speaking to the council from the city of Port Sudan.

The envoy said he is in regular contact with rival generals who are battling for control of the north-east African country, where heavy fighting broke out more than a week ago.

De facto president Abdel Fattah al-Burhan, who is also commander-in-chief of the army, is fighting with the military against his deputy Mohammed Hamdan Daglo, the leader of the powerful paramilitary group Rapid Support Forces (RSF).

The two men have led the gold and oil-rich country of some 46 million people since a military coup in 2021.

According to information from the World Health Organization (WHO), at least 460 people have been killed and almost 4,100 injured in the fighting. The true figure, however, is likely to be much higher.

Perthes said a 72-hour US-brokered ceasefire that went into effect on Tuesday was holding in "parts" of the country, but that clashes had escalated in others.

Fighting has "largely continued or in some cases intensified" around Khartoum's international airport, the official residence of the president, military sites and other strategic locations, he said.

Airstrikes and heavy shelling have also continued, especially in the cities of Khartoum Bahri and Omdurman.

As food and water supplies run low amid supply line disruptions, there were also numerous reports of homes being broken into, houses and shops looted, and cars stolen at checkpoints.

"We have also received disturbing reports of attempted sexual assaults," the envoy said.

The fighters have shown "little consideration for civilians, for hospitals, or even for vehicles transferring the wounded and sick."

Evacuation flights of foreign nationals continued. France reported flying 538 people out of Sudan, while the Dutch Foreign Ministry said it had taken around 120 people out of the country.

The British government began evacuation flights for civilians from Sudan on Tuesday.

Germany's armed forces planned to end its mission in Sudan to evacuate Germans and citizens of other nations on Tuesday. The air force has evacuated a total of more than 600 people on six flights in recent days.

Meanwhile, a WHO spokesman said that a central medical laboratory had been occupied by fighters. The staff had been thrown out.

The WHO representative in Sudan, Nima Saeed Abid, warned that biological material was stored in the laboratory and should not be released under any circumstances.

Medical care also came under increasing pressure. A Red Cross material warehouse had been looted, reported the representative of the Federation of Red Cross and Red Crescent Societies (IFRC), Farid Aiywar. As a result, hospitals can hardly be supported with medicines and other material.