Three aid workers from Médecins sans Frontières Belgium are being held hostage after being kidnapped in Darfur, a spokeswoman said today.

Five staff were seized in Serif Umra, in the Sudanese province of North Darfur, but two – both Sudanese – were later released, MSF said.

A Canadian nurse, an Italian doctor and a French project co-ordinator are still being held. "We have no information about the missing workers' whereabouts or the motives for the abduction," an MSF spokesperson said in Nairobi. The agency said later that it would withdraw all medical teams from projects in Darfur and would leave only an "essential skeleton team", who would try to secure the freedom of the staff being held hostage. "MSF is extremely worried both for our abducted colleagues and for the populations that MSF teams had been providing medical aid to," the agency said in a statement.

The staff were seized at about 8pm GMT yesterday, Ahmed Salah, a spokesman for the United Nations African Mission in Darfur (Unamid), said.

The immediate relatives of those still held hostage have been informed.

"Our thoughts are with the colleagues and families of those abducted," the MSF spokeswoman said.

"MSF is deeply concerned about their safety and is doing everything it can to determine their whereabouts and ensure their safe and swift return."

While both pro-and-anti government militias in Darfur often hijack aid vehicles and have previously kidnapped humanitarian workers, the timing will raise questions of possible state involvement.

The abductions came exactly a week after the international criminal court (ICC) issued an arrest warrant for Sudan's president, Omar el Bashir, for alleged war crimes in Darfur. In response, the government expelled 13 international aid agencies and three local organisations, having warned some of them a few days before that it could not guarantee their security.

Workers from the Dutch section of MSF were expelled from Darfur by the Sudanese government. MSF France also had its licence revoked. MSF expressed outrage at the decision, which it said would leave more than 200,000 patients without essential medical care.

The UN estimates the expelled organisations, which also include Care, Oxfam and Save the Children, carried out about half of all the relief work in Darfur, where 4.7 million receive aid. It has warned of a possible humanitarian crisis if the government does not immediately reverse its decision.

But Sudan, which accuses the aid agencies of spying for the ICC, has dismissed the fears, suggesting that non-Western humanitarian organisations could fill the gap.

"We have received many applications from Arab and Asian countries. They want to go to Darfur," said Ahmad Harun, Sudanese State Minister for Humanitarian Affairs, who is also sought by the ICC, on 51 charges of war crimes and crimes against humanity.

Most of the expelled agencies have withdrawn their international staff from Sudan, following threats and harassment. Last week, government officials interrogated dozens of foreign aid workers after examining seized computer records. The government has also frozen the agencies' bank accounts, and confiscated all assets, from mobile phones to 4x4 vehicles.

One aid agency, which asked not to be named, said though it was officially still appealing the expulsion order it was resigned to quitting Sudan.