The UN's most senior humanitarian official has warned that Sudan's Darfur region faces a new humanitarian disaster owing to lack of security.
Egeland said violence, sexual abuse and displacement had increased
Jan Egeland spoke as the Security Council considered a US and UK plan to send about 17,500 UN troops to Darfur.
He called for "immediate action" on the political front, to avoid a humanitarian catastrophe threatening "massive loss of life".
Sudan rejects transforming an existing African Union force into a UN mission.
Some 200,000 people have been killed and more than 2m driven from their homes in three years of fighting in Darfur.
In May, the Sudanese government agreed a peace deal with a faction of the Sudan Liberation Army, one of the main regional rebel groups.
But Mr Egeland warned the Security Council that since the peace deal there had been a dramatic increase in violence, sexual abuse and displacement in Darfur.
"Insecurity is at its highest levels since 2004, [humanitarian] access at its lowest levels since that date and we may well be on the brink of a return to all-out war," Mr Egeland told the council, according to a text of his remarks quoted by Reuters news agency.
Sudan boycotts meeting
The US envoy to the UN, John Bolton, said he wanted a new Security Council resolution "in the next couple of days" authorising a UN force to be sent to Darfur.
AU forces in Darfur are stretched beyond capacity
The force, envisaged to encompass some 17,500 UN troops plus some 3,000 UN police, would replace some 7,000 African Union troops due to leave Darfur on 1 October.
Mr Bolton told reporters the main sticking point was the lack of consent from the Sudanese government - which boycotted the Security Council meeting.
The Sudanese government wants to send at least 10,000 of its own troops to Darfur, and human rights organisations allege it is already flying soldiers into the region.
The organisations say allowing Khartoum to send in its own force could see an escalation of the violence in the region.
But Sudanese National Congress Party chairman Ghazi Salah Eldin Atabani said the plan for a UN force would "impose complete tutelage" on Sudan.
"Any state that sponsors this draft resolution will be regarded as assuming a hostile attitude against the Sudan," he said.
Meanwhile, US Assistant Secretary of State Jendayi Frazer has announced she is staying in Sudan an extra day in order to try to meet President Omar al-Bashir.
Mrs Frazer, who was due to have left Khartoum on Monday, brought with her a letter from President George W Bush aiming to persuade the Sudanese government to authorise the deployment of a UN peace force in Darfur.
She has not yet met President Bashir as she had intended, and her visit began badly on Saturday when she was met at the airport by an angry mob shouting "go home".