More than 100,000 people have fled Sudan since heavy fighting broke out between rival forces on 15 April, the UN has said.
Officials warned of an "all-out catastrophe" if fighting does not end.
A further 334,000 people have been displaced within Sudan.
Fighting is continuing in the capital, Khartoum, between the army and the paramilitary Rapid Support Forces (RSF), despite a ceasefire due to be in force.
On Monday, the UN special envoy to Sudan, Volker Perthes, told the AP news agency that the two sides had agreed to enter into talks to negotiate a "stable and reliable" ceasefire.
Saudi Arabia was a potential venue for the talks, he added.
If talks take place, it would be the first meeting between the two sides since the conflict started.
More than 500 people have been killed and more than 4,000 have been wounded in the fighting, according to Sudan's health ministry.
A series of temporary ceasefires have failed to hold, with the military continuing to pound Khartoum with air strikes in a bid to weaken the RSF.
Heaving fighting has also taken place in Darfur in western Sudan.
UNHCR spokeswoman Olga Sarrado told reporters in Geneva that the 100,000 total included people from Sudan, South Sudanese citizens returning home, and people who were already refugees within Sudan fleeing the fighting.
Refugees have also been fleeing over Sudan's border with Egypt in the north and Chad in the west.
Most European states have completed the evacuation of their nationals, but Russia said on Tuesday that it was sending four military planes to fly out more than 200 people - including its nationals and those from "friendly countries" - from Sudan.
In Khartoum, food, water and electricity are running out, but desperately needed aid supplies - shipped by the UN into Port Sudan - are being warehoused because of the violence. Meanwhile, widespread looting means there is no safe way to deliver them.
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