UNITED NATIONS – Secretary-General Ban Ki-moon called Sudan's president to seek help in freeing two members of the joint United Nations-African Union peacekeeping mission in Darfur who have been held hostage for more than 100 days, the U.N. said Monday.

U.N. spokesman Martin Nesirky said it was the first call between the secretary-general and Omar al-Bashir since the International Criminal Court issued an arrest warrant for the Sudanese leader in March on charges of orchestrating war crimes and crimes against humanity in Darfur.

Ban's phone call Sunday came two days after Luis Moreno-Ocampo, the court's chief prosecutor, said the Sudanese leader was becoming increasingly isolated and will ultimately face international justice. Al-Bashir has refused to recognize the tribunal's authority.

The war in Darfur began in 2003 when rebel groups took up arms against the government, complaining of discrimination and neglect. U.N. officials say up to 300,000 people have died and 2.7 million have fled their homes.

Nesirky emphasized that the call was made purely on humanitarian grounds, noting that one of the two abductees is "gravely ill." The two staffers, a man and a woman, were abducted at gunpoint in West Darfur on Aug. 29.

The secretary-general wanted to ensure that all efforts are being made to secure their release, Nesirky said.

"The government has been attempting to secure their release but they have not as yet been released," he said. "The president assured the secretary-general that everything possible was being done."

The secretary-general and the U.N. Security Council also condemned two separate attacks Friday and Saturday on peacekeepers with the U.N.-AU force, known as UNAMID, that killed five Rwandan soldiers.

The council statement on Monday noted the action taken already by the Sudanese government "and encouraged it to ensure that all the perpetrators are swiftly identified and brought to justice."

The secretary-general noted the deteriorating security situation in Darfur and called on the government to do its utmost to ensure that the perpetrators are swiftly identified and brought to justice.

The Security Council reiterated its full support for UNAMID and called on all parties in Darfur "to cooperate fully with the mission, including to secure the release of the two staff held hostage."