Map of Darfur region of Sudan

The United Nations secretary-general has expressed concern over recent reports of aerial bombings in Sudan's war-torn Darfur region.

In a statement Wednesday, Ban Ki-moon says he has received troubling reports of attacks near Kutum in North Darfur, and also of fighting in the Tine area near the border with Chad.

Mr. Ban is calling on all parties to refrain from hostilities and respect the spirit of the cease-fire declared by Sudan's president. He asked all parties to cooperate with the United Nations-African Union Mission in Darfur in investigating the reported attacks.

Last week, Sudanese President Omar al-Bashir pledged an "immediate and unconditional" cease-fire in Darfur. However, shortly after the announcement, government and rebel forces accused each other of violating the truce.

The president has announced several cease-fires during the nearly six-year Darfur conflict. All of them have failed.

Human rights activists say the conflict in Darfur, involving rebels, government forces and pro-government militias, has killed more than 200,000 people and driven more than 2.5 million from their homes. Sudan's government says these numbers are exaggerated, and it puts the death toll at about 10,000.

Some information for this report was provided by Reuters.