United Nations (CNN) -- The U.N. chief phoned Sudanese President Omar al-Bashir, who has been charged with crimes against humanity, for the "sole purpose of an urgent humanitarian matter," the international body said Monday.
Ban Ki-moon urged al-Bashir to use "direct engagement" in securing the release of a man and a woman who have been held hostage for 100 days -- one of whom has fallen "gravely ill." The pair were part of the joint United Nations-African Union Mission in Darfur when they were abducted at gunpoint on August 29.
"The situation is critical," U.N. spokesman Martin Nesirky told reporters at a Monday briefing.
"The president assured the secretary-general that everything possible was being done," he added.
The U.N. chief's phone call on Sunday to al-Bashir followed two deadly attacks on UNAMID peacekeeping forces in the Darfur region of Sudan on Friday and Saturday. Five Rwandan peacekeepers were killed in the attacks, bringing to 22 the total number of people lost since the mission was deployed in 2008.
Ban urged the government of Sudan to swiftly identify and bring the perpetrators to justice, and shared his appreciation for the service of the victims in "the search for peace in Darfur."
"President al-Bashir indicated he had issued instructions to his security agencies that the perpetrators be apprehended as soon as possible," Nesirky said.
Members of the U.N. Security Council condemned the attacks and expressed condolences to the families of those killed and the Rwandan government, according to a statement read by Security Council President Michel Kafando.
The Security Council also noted and encouraged the action taken by the Sudanese government, but looked to all parties in Darfur "to cooperate fully with the mission."
The weekend attacks coincided with a Security Council briefing Friday by the International Criminal Court's chief prosecutor on the continuing violence in Darfur and the lack of cooperation with investigators by al-Bashir and his government.
Luis Moreno-Ocampo highlighted the role played by the Sudanese president in what he said are the ongoing crimes in Darfur, which include "indiscriminate bombings of civilians" and the "use of child soldiers."
The International Criminal Court has issued a warrant for al-Bashir's arrest for war crimes and crimes against humanity.