The United Nations refugee agency says it estimates that more than 700,000 refugees will flee Sudan Sudan by the end of the year, more than double the number forecast just a few months ago.
The agency says it is seeking more that $650 million to help the refugees, a large revision from March, when the agency requested about $370 million in aid.
It says Ethiopia is witnessing the biggest surge in refugee arrivals over recent months, with 1,000 refugees a day crossing into the remote town of Burubiey.
The refugees are fleeing fighting that erupted in December between forces loyal to President Salva Kiir and military factions aligned with his former deputy, Riek Machar. The violence has killed at least 10,000 people.
Also Friday, the aid group Save the Children said an outbreak of cholera in South Sudan has infected more than 2,600 people and killed at least 60 since May. A spokeswoman for the group, Olivia Zinzan, said suspected new cases are being reported on an almost daily basis.
"And in fact, there's been suspected cases reported in nine out of the 10 states in South Sudan. This is an extremely worrying trend, coming as it does on top of multiple emergencies that the country is facing," she said "There's been over 1.5 million people who've been displaced from their homes by the fighting over the last seven months, and on top of that the country's on the brink of famine in many parts as a hunger crisis takes grip on the state."
In another development, the European Union issued a travel ban on Friday and an asset freeze on a rebel leader and government commander in South Sudan, saying they have committed atrocities and obstructed the peace.
The EU accused rebel leader Peter Gadet of leading an attack on the town of Bentiu in May, which violated a cease-fire deal and left 200 civilians dead. Government commander Santino Deng is accused of leading an offensive to retake Bentiu from rebel forces.