(CNN) -- Three Doctors Without Borders (Medecins Sans Frontieres) staffers have been abducted in the war-torn Sudanese province of Darfur, the group said Thursday.
Aid groups have been told to leave Sudan after an arrest warrant was issued for President Omar Hassan al-Bashir.
A Canadian nurse, an Italian doctor and a French coordinator were abducted Wednesday night.
Two Sudanese workers had also been taken, but they have since been freed, the group said. The incident took place in Serif Umra, the Sudanese province in northern Darfur.
The three were working for the group's Belgian section and their relatives have been contacted.
At present, the group is trying to determine "the circumstances and the motives" of the abduction.
"Our thoughts are with the colleagues and families of those abducted. MSF is deeply concerned about their safety and is doing everything it can to determine their whereabouts and ensure their safe and swift return," the group said.
Sudan last week ordered 13 major aid groups to leave the country after an arrest warrant was issued for President Omar Hassan al-Bashir. The International Criminal Court issued the warrant for war crimes and crimes against humanity. It accuses him of complicity in a brutal campaign of violence against the people of Darfur.
Two of MSF's sections -- one run by the Dutch and one run by the French -- were ordered out. They were also operating in Darfur. Along with the Belgian section, there are other teams in the country.
MSF is an international medical group that works in more than 60 countries. It helps people "threatened by violence, neglect, or catastrophe."
The United Nations on Wednesday announced the start of a joint U.N.-Sudanese government mission "to evaluate the need for food, water, health and emergency shelter in Darfur" amid the expulsions of the groups, which are believed to have assisted about 4.7 million people.
As of Tuesday, 183 international staffers of the affected nongovernmental organizations have left Sudan and others are awaiting exit visas to depart, the U.N. Office for the Coordination of Humanitarian Affairs said.
The United Nations says that along with Darfur, other areas in the country will be affected by the expulsions, citing Abyei, Blue Nile State, and Southern Kordofan State -- locations "on the front lines of the North-South civil war." Some of the expelled workers "provided health, nutrition, water, sanitation, education, food security and other assistance to hundreds of thousands of people there. "
The United Nations estimates that 300,000 people have died in Darfur, where government forces and Arab militia allies have been fighting rebels. People have died "either through direct combat or because of disease, malnutrition or reduced life expectancy," and around 3 million people have been displaced since 2003.
Meanwhile, there have been diplomatic developments.
Representatives of Sudan's government and the rebel Justice and Equality Movement have "recommitted themselves to a negotiated settlement to the conflict," the United Nations said.
Djibril Bassole, the U.N.-African Union joint chief mediator, plans to meet with the representatives of other rebel movements and regional countries in the coming days" and is "to brief the U.N. Security Council on the Darfur political process on March 26."
-- CNN's Joe Sterling contributed to this report.