Gunmen abducted two female aid workers in Darfur on Friday, said the international peacekeeping mission in the western region of Sudan.
It was the third kidnapping of foreign humanitarian workers since March, when an international court issued a warrant for the country's president on charges of orchestrating war crimes in Darfur.
The series of abductions, along with Sudan's expulsion of 13 international aid agencies in response to the arrest warrant, has struck a blow to the vital aid effort in the remote desert region, now in its sixth year of conflict.
The two women seized Friday from their compound in the Kutum region of north Darfur work for an Irish aid group called GOAL, said Noureddine Mezni, a spokesman for the United Nations-African Union peacekeeping force.
One of the women is Irish and the other is Ugandan, he said. The aid group has been working in Darfur since 2004. A phone call to the aid group in Ireland went unanswered Friday night.
The peacekeeping mission appealed for their release, saying they were in Darfur to help its people.
Sudan's Arab-dominated government has been battling ethnic African rebels in Darfur since 2003. Up to 300,000 people have been killed and 2.7 million have been driven from their homes. The Sudanese government denies accusations that it responded to the uprising by unleashing militiamen who have carried out attrocities against civilians.
The International Criminal Court in The Hague, Netherlands, issued the arrest warrant for President Omar al-Bashir in March on charges of war crimes and crimes against humanity for allegedly orchestrating efforts to wipe out three African tribes in Darfur.
Al-Bashir dismissed the charges and responded by expelling some of the most important aid agencies, which he accused of spying for the court.
Days later, gunmen seized three foreign aid workers for the Belgian branch of Doctors Without Borders, also known as Medicins Sans Frontieres. They were released after three days.
An area governor said at the time that the kidnapping was carried out by a group seeking to retaliate for the arrest warrant against al-Bashir.
In April, two female aid workers with International Medical Aid - one French, the other Canadian - were kidnapped in southern Darfur. They were released three weeks later.
The abduction of international aid workers was unprecedented in Darfur, though bandits had robbed trucks carrying aid supplies, often disappearing with the vehicles and their Sudanese drivers.