2 South African soldiers killed by a mortar explosion in eastern Congo amid unrest

Two South African soldiers were killed and three injured when a mortar landed in their base in eastern Congo amid increased unrest in the region, the South African armed forces said Thursday.

The South African National Defence Force, which oversees all of the country's armed forces, said it believed the mortar explosion on Wednesday was a result of "indirect fire" and an investigation was underway to determine who was responsible.

South Africa has sent soldiers to Congo as part of the Southern African Development Community's mission to fight against armed rebel groups in the east.

South Africa announced this week it would be sending a new contingent of 2,900 soldiers to eastern Congo. It wasn't immediately clear if those killed and injured were part of that new deployment.

The base that was hit was in the North Kivu province, South African National Defence Force spokesperson Siphiwe Dlamini said. The injured were taken to a hospital in the city of Goma.

Violence in the conflict-hit region has increased in recent weeks, with many blaming attacks on the M23 rebel group that has been fighting Congolese soldiers in the region for years.

The Congo government says M23 is receiving military support from neighboring Rwanda, which Rwanda denies.

But M23 has indicated in recent statements that it is in the midst of a new advance in eastern Congo, leading to fears the group is again targeting Goma, which it once seized 10 years ago.

More than 1 million people have been displaced by the conflict since November, aid groups say. That adds to the 6.9 million who already fled their homes in one of the world's biggest humanitarian crises.

On Thursday, the Norwegian Refugee Council said the recent advance of armed groups toward the key town of Sake, near Goma, "poses an imminent threat to the entire aid system" in eastern Congo.

"The isolation of Goma, home to over 2 million people and hosting hundreds of thousands of displaced individuals who have fled clashes with armed groups, would bring disastrous consequences to the region," the NRC said.