UNITED NATIONS - UN Secretary-General Ban Ki-moon on Friday voiced his deep concern at the "continuing tensions" in the border area between Sudan and South Sudan, and called on the parties concerned "to do everything possible to reach agreement" in their current talks.

"The secretary-general is deeply concerned by continuing tensions along the border between Sudan and South Sudan as well as the current oil crisis," said a statement issued here by Ban's spokesman. "This situation indicates a worrying deterioration in the relationship between the two states."

"The United Nations fully supports the efforts of the African Union High Level Implementation Panel (AUHIP) to resolve these and other outstanding issues between the parties based on the concepts of mutual viability, security and peaceful coexistence," the statement said.

"The secretary-general strongly urges the parties to do everything possible to reach agreement in their current negotiations in Addis Ababa under the auspices of the AUHIP, to defuse the current oil crisis, and address the other contentious issues on the agenda that require immediate resolution," the statement said.

The secretary-general's special envoy, Haile Menkerios, remains on the ground, engaging to assist the negotiations in collaboration with the AUHIP, the statement said.

In the South Sudanese capital of Juba on Friday, Johnson said, "The ongoing security crisis in Jonglei state is a test for all of us."

"All concerned should redouble their efforts to put an immediate end to the cycle of violence, which is putting thousands of lives at risk and threatening the stability of the whole area," said Johnson, who is also the head of he UN Mission in South Sudan (UNMISS).

Fighting between Lou Nuer and Murle communities, which have a history of conflict over land and resources for cattle grazing, escalated sharply in late December, causing an estimated tens of thousands people to flee their homes in Pibor County and resulting in casualties, destruction of property and livelihoods.

Retaliatory attacks were then launched on communities in Akobo, Uror and Duk counties. The most recent attack took place on January 16, when 80 people were reportedly killed and 300 houses burnt in Duk Padiet in Duk County, according to local authorities.

The recent spike in inter-communal violence has compounded an already difficult humanitarian situation in South Sudan, Office for the Coordination of Humanitarian Affaris (OCHA) stated. Aid agencies were already supporting 30 simultaneous emergency operations before the crisis in Jonglei began, where confrontations between the Murle and Lou Nuer peoples often took place.

Since mid-2011, tensions on the border with Sudan have also escalated, triggering fresh displacements. In May 2011, violence erupted in Abyei, displacing 110,000 people into Agok and South Sudan where they remain displaced.