KHARTOUM (Reuters) - Three international aid workers from Medecins Sans Frontieres have been kidnapped in Darfur, officials said on Thursday, further complicating humanitarian operations in Sudan's west.

The three workers from the medical charity's Belgian arm were seized alongside two Sudanese as tension escalated in Sudan following the International Criminal Court's decision this month to issue an arrest warrant for Sudanese President Omar Hassan al-Bashir over accusations of war crimes in Darfur.

We can confirm that a group of armed men went to the location and ordered five persons to follow them. They were three international staff and two national staff, said Kemal Saiki, communications director for the United Nations-African Union peacekeeping force in Darfur, known as UNAMID.

Medecins Sans Frontieres (MSF) in Belgium said the two Sudanese were quickly released but the three foreigners were still held. It identified them as a Canadian nurse, an Italian doctor and a French coordinator.

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

Sudan shut down 16 aid organizations after the ICC decision, saying they had helped the court in the Hague, an accusation aid groups deny. Two arms of MSF were among those asked to leave, although MSF Belgium was not among them.

MSF said it would withdraw most staff from Darfur where conflict has simmered since mostly non-Arab rebels took up arms against the government in 2003. International experts say at least 200,000 people have been killed in the mainly desert western region, while Khartoum says 10,000 have died.

Sudan's foreign ministry condemned the kidnappings, and said the abducted aid workers were thought to be in good health and had not been harmed.

I promise this conduct will never be repeated. I want to confirm that the government is ready to provide security for all the NGOs, the head of Sudan's Humanitarian Aid Commission, Hassabo Mohamed Abd el-Rahman, told reporters. He said he believed money may have been a motive.

MORE VIOLENCE IN DARFUR?

The kidnapping took place in Saraf Omra in north Darfur, where MSF Belgium runs a health clinic and dispensary serving tens of thousands of people, said Susan Sandars, an MSF spokeswoman in Nairobi, Kenya. UNAMID said the kidnapping took place late on Wednesday, while Sudan said it was on Thursday.

Some analysts say the ICC warrant against Bashir could spark more violence in Darfur, where civilians and peacekeepers have been caught in the middle of the conflict. Aid officials have said they feared humanitarian workers could be targeted.

This is a game-changing scenario, said one aid worker who declined to be named, referring to the abductions. If the worse case happens, Darfur is going to be a totally different environment for us.

Speaking on Wednesday before the abductions, MSF Belgium's Operations Director Stephan Goetghebuer told Reuters his staff in Darfur had faced growing antagonism in the days after the global court's announcement.

MSF has never collaborated with the ICC. Yet, it's obvious that part of the population in Sudan took these accusations about NGOs very seriously, he said.

Before the expulsions, the United Nations and aid groups were running the world's largest humanitarian operation in Darfur. U.N. agencies have said they could not fill the gap left by NGO partners who handed out food, monitored for diseases, and provided clean water and healthcare across Darfur.

In one speech last week Bashir said the expelled groups were spies and thieves, and a pro-government newspaper printed a photo of one international aid worker, saying the officer was an intelligence officer for Israel, an arch-foe of Sudan.

(Reporting by Andrew Heavens and Khaled Abdel Aziz in Khartoum, Emma Bath via Alertnet and Philip Blenkinsop in Brussels; Writing by Cynthia Johnston; Editing by Katie Nguyen)

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