GOMA, Congo (AP) — Two staff members of the foreign aid group Tearfund were killed when their convoy was attacked in eastern Congo, the organization said, the latest in a series of violent attacks targeting aid groups and residents in the region.

The aid workers were killed on Sunday after their convoy had arrived in Butembo city in the North Kivu province where armed rebels have been fighting Congolese security forces, the organization said in a statement late Monday.

It wasn't immediately clear which group was behind the attack, but more than 120 armed groups in eastern Congo have been carrying out deadly attacks that often involve bombs targeting residents as they seek a share of the region’s gold and other resources.

The violence in the province has worsened in recent months as security forces battle the rebels. Two people were killed last week in the region when mortar shelling targeted a base operated by South Africa’s military, which is part of a regional peacekeeping mission. The rebels have also overtaken more villages in recent weeks.

The M23 rebel group, with alleged ties to neighboring Rwanda, has been the most active in the region, seizing strategic towns, with about half of the North Kivu province under their control, according to Richard Moncrieff, the Crisis Group’s Great Lakes region director.