UN aid chief warned that the situation in Darfur was "rapidly spiralling into a humanitarian calamity".
Sudan's devastating war raged on into a third month Thursday as the reported death toll topped 2,000 and after a state governor was killed in the remote Darfur region.
Since April 15, the regular army headed by Abdel Fattah al-Burhan has been locked in fighting with paramilitary Rapid Support Forces (RSF) commanded by his former deputy Mohamed Hamdan Daglo.
The fighting has driven 2.2 million people from their homes, including 528,000 who have fled to neighbouring countries, says the International Organization for Migration.
"In our worst expectations, we didn't see this war dragging on for this long," said Mohamad al-Hassan Othman, among more than one million civilians who have fled heavy fighting in the capital Khartoum.
Everything in "our life has changed," he told AFP.
"We don't know whether we'll be back home or need to start a new life."
The death toll has risen above 2,000, according to the Armed Conflict Location and Event Data Project's latest figures which cover fighting until June 9.
In long-troubled West Darfur state, the violence claimed the life of Governor Khamis Abdullah Abakar, hours after he made remarks critical of the paramilitaries in a telephone interview with a Saudi TV channel.
The United Nations said compelling eyewitness accounts attribute this act to Arab militias and the RSF, while the Darfur Lawyers Association condemned the act of "barbarism, brutality and cruelty".
Burhan accused his paramilitary foes of the "treacherous attack". The RSF denied responsibility and said it condemned Abakar's "assassination in cold blood".
Sudan analyst Kholood Khair of the Khartoum-based think tank Confluence Advisory said the "heinous assassination" was meant "to silence his highlighting of genocide... in Darfur".
UN aid chief Martin Griffiths meanwhile warned that the situation in Darfur was "rapidly spiralling into a humanitarian calamity".
"The world cannot allow this to happen. Not again," he said in a statement, describing the reality there as a "living nightmare".
US and Saudi mediation efforts are at a standstill after the collapse of multiple ceasefires in the face of flagrant violations by both sides.
The East African Inter-Governmental Authority on Development (Igad) has attempted to restart discussions, announcing this week that Kenya would chair a quartet including Ethiopia, Somalia and South Sudan tasked with resolving the crisis.
In a statement Thursday, the foreign ministry, loyal to Burhan, "objected to Kenya's chairmanship", alleging that Nairobi had "adopted the positions of the RSF militia, sheltered its people and offered them various forms of support".
The office of Kenyan President William Ruto -- who has met both RSF and army senior officials in recent weeks -- had released a draft communique of the Igad meeting that said quartet leaders would "arrange (a) face-to-face meeting between (Burhan and Daglo)... in one of the regional capitals."
A Sudanese official told AFP on condition of anonymity because they are not authorised to speak to the media, that Burhan "will not sit at the same table" as Daglo, as fighting shows no signs of abating.
A record 25 million people -- more than half the population -- are in need of aid, according to the UN, which says it has received only a fraction of needed funding.
Saudi Arabia has announced an international pledging conference for next week.
"We have nothing left," said another person living in the capital, Ahmed Taha. "The entire country has been completely devastated... Every inch of Sudan is a disaster area."
Many of the displaced have lost loved ones as well as "all their belongings and livelihoods", said Anja Wolz of aid group Doctors Without Borders.
Darfur, one of the war's main battlegrounds, was already scarred by a two-decade conflict that left hundreds of thousands dead and more than two million displaced.
Daglo's RSF have their origins in the Janjaweed militias which former strongman Omar al-Bashir unleashed on ethnic minorities in the region in 2003, drawing charges of genocide, war crimes and crimes against humanity.
Homes and markets have been burnt to the ground, hospitals and aid facilities looted and more than 149,000 people sent fleeing into neighbouring Chad.