Two South African peacekeepers were wounded when gunmen opened fire on their patrol in Sudan's troubled Darfur region.

The soldiers were injured when unidentified attackers shot at them as they collected water in the Kutum district of North Darfur state on Wednesday, the joint United Nations African Union mission said.

The troops returned fire and the casualties were "evacuated to el-Fasher for treatment" in the state capital, UNAMID press officer Guiomar Pau said.

It was unclear who the attackers were, she said, or whether any were hit by the return fire.

The injured soldiers were airlifted by helicopter to the hospital in el-Fasher shortly after the ambush Captain Jaco Theunissen

A spokesperson for the South African National Defense Force (SANDF) said the soldier were in a critical but stable condition in a UN hospital.

"The injured soldiers were airlifted by helicopter to the hospital in el-Fasher shortly after the ambush," Captain Jaco Theunissen said.

The SANDF currently have 809 members including eight military observers and seven staff officers in Sudan.

UNAMID was deployed in late 2007 to help end bloodshed among militias, rebel forces and gangs in Darfur.

Three Ethiopian peacekeepers were killed on October 16 as they guarded a well in Karma in North Darfur.

Violence in Darfur which UNAMID has attributed to government-linked forces, rebel offensives and inter-communal fighting has risen this year to its worst level in a decade.

More than 300,000 people have been killed in some 11 years of conflict in the region, with another two million displaced, the UN said.