Updated

Armed men stormed an aid agency compound in Darfur and kidnapped three Westerners, heightening fears that foreigners will be targeted in the backlash over the international arrest warrant for Sudan's president.

The three workers for Doctors Without Borders were kidnapped late Wednesday in a government-controlled area in northern Darfur, close to a stronghold of government-allied Arab militiamen known as janjaweed.

The Sudanese government condemned the attack and denied any involvement. But officials quickly blamed the arrest warrant issued last week by the Netherlands-based International Criminal Court accusing President Omar al-Bashir of war crimes in Darfur.

"Anything that goes wrong (since the warrant) onwards I personally attribute to the ICC decision," Foreign Ministry spokesman Ali Youssef said.

Ali Sadiq, another Foreign Ministry official, told Al-Jazeera television that his ministry had warned that the warrant "encourages lawlessness and armed groups to target aid groups and their workers."

Late Thursday, a state-linked media organization said the kidnappers had demanded a ransom. Quoting the governor of North Darfur, the Sudan Media Center said local government officials had begun negotiations.

"The kidnappers asked for a ransom and they reassured us that they don't want violence," Gov. Osman Kebir was quoted as saying. The report did not say how much money was demanded.

Kebir said he had phoned the kidnappers at a number sent to him by the abductors and also had spoken with the captives, who said they were in good condition, according to the report.

Al-Bashir's government has been warning since even before the warrant was issued March 4 that the case could lead to revenge attacks by Sudanese, though it said it would try to protect aid workers, peacekeepers and other foreigners.

Sudan has vehemently denounced the warrant as a "colonialist" attempt to destabilize the country. After it was announced, Khartoum retaliated by expelling the 13 biggest aid groups working in Darfur, accusing them of helping the court.

The expulsion has sparked fears of a humanitarian crisis in the region, where the government and rebels have been fighting for six years and several million people rely on international agencies for food, shelter and water.

The Dutch and French branches of Doctors Without Borders, also known as Medecins Sans Frontieres, or MSF, were among the expelled aid groups. But the abducted staffers belonged to its Belgian branch, which was allowed to remain along with the Spanish and Swiss branches and dozens of other smaller aid groups.

MSF said Thursday that because of safety concerns all its branches would move their personnel out of Darfur to Khartoum — except for a small number working for the abducted staffers' release.

"Evacuation will mean an interruption to many of MSF's essential medical services in Darfur. MSF is extremely worried both for our abducted colleagues and for the populations that MSF teams had been providing medical aid to," the group said in a statement.

Earlier this week, the U.S. Embassy in Khartoum authorized the departure of nonessential staff, saying the security situation was "uncertain."

Several Islamic fundamentalist groups and a militia in Darfur have made public threats to attack ICC supporters in Sudan. The threat was dismissed by Sudanese officials as an expression of "political support" for al-Bashir.

In the Wednesday evening attack, gunmen entered the compound where the MSF-Belgium staffers lived and worked in the rural town of Saraf Umra, 125 miles west of the regional capital El Fasher, said Susan Sandars, an MSF spokeswoman in Nairobi, Kenya. The clinic provides vaccinations, treatment for malnutrition and prenatal care.

The gunmen seized a Canadian nurse, an Italian doctor and a French coordinator, along with two Sudanese guards who were released several hours later, Sandars said. It was not clear if violence was used in the abduction.

Banditry, break-ins and carjackings against aid organizations have long been common in Darfur, usually blamed on the many armed groups operating in the region. Worsening lawlessness in the past year forced many aid workers to travel only by helicopter to avoid high-risk roads.

Sudanese aid workers have been killed in such attacks. Others have been held by attackers, with most quickly freed after being stripped of their vehicles, equipment or cash.

The latest attack was different. "Deliberately going to some place with the intention of taking people away" has not been seen before, said Kemal Saiki, communication director for the joint United Nations-African Union peacekeeping mission in Darfur.

The attackers likely faced little or no resistance since security around such compounds is often not strong, Saiki said.

The three captives were allowed by the kidnappers to call MSF colleagues to assure them they are in good health, said Hassabo Abdel-Rahman of Sudan's government humanitarian affairs office. The captives said that "they are eating and drinking and are OK," he told reporters.

The two released Sudanese guards were questioned by police but could not identify their abductors, Abdel-Rahman said.

"It's an isolated and immoral act," the spokesman said.

A Darfur rebel group, Sudan Liberation Movement-Unity, accused the government of being behind the kidnapping, saying authorities were trying to create "a security vacuum" in Darfur.

Four peacekeepers were wounded in an ambush in western Darfur only days before the abduction. The attackers were never identified.

The ICC warrant accuses al-Bashir of orchestrating atrocities against civilians in Darfur, where his Arab-led government has been battling ethnic African rebels since 2003. Up to 300,000 people have been killed, and 2.7 million have been driven from their homes.