The IOM warned in a statement that 1.8 million more are expected to be internally displaced if the war persists.
It noted that there were 1.1 million refugees and 3.8 million internally displaced people in the country before the conflict.
While nearly 259,000 people have already escaped from Sudan to nearby countries, it said that over a million refugees and migrants impacted by the turmoil may move to neighboring countries if the conflict continues.
According to the organization, humanitarian aid is currently projected to be needed by over 25.7 million people both inside and outside Sudan.
The IOM also created a response plan and made an appeal for $209 million in order to provide critical humanitarian assistance to those impacted by the crisis.
The appeal includes the urgent need of $105 million for Sudan and $104 million for the response in Egypt, Libya, Chad, Central African Republic, South Sudan and Ethiopia, it said.
"The current humanitarian situation in Sudan is by far the worst the country has ever seen," IOM Director General Antonio Vitorino said in the statement.
"Millions are in pressing need of basic assistance such as water, food and shelter. If we do not act NOW, the people of Sudan will face an inevitable humanitarian catastrophe," Vitorino said.
"We appeal to the international community to urgently support relief efforts and mobilize financial resources to meet the mounting needs."
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