South Sudanese President Salva Kiir has spoken with his Sudanese counterpart Omar al-Bashir in a bid to ease tensions after deadly clashes in Abyei, a region claimed by both sides, officials said Monday.
UN chief Ban Ki-moon and the African Union have appealed for calm in the flashpoint area after the killing of a tribal chief and a UN peacekeeper on Saturday.
"Our president has been in direct contact with president Bashir... they exchanged ideas about this sad incident," South Sudan's Information Minister Barnaba Marial Benjamin told reporters.
Both Juba and Khartoum have condemned the fighting which killed Kual Deng Majok, the Abyei leader of the Dinka Ngok, a people viewed as loyal to South Sudan.
Majok and an Ethiopian peacekeeper were shot dead in an attack by gunmen from the Misseriya, a pastoralist people who graze their cattle in Abyei and are seen as supporters of Khartoum.
Several Misseriya are also reported to have been killed, as well as a Dinka colleague of Majok. Two peacekeepers were also wounded.
Ban urged both sides to "avoid any escalation of this unfortunate event," while the AU, which has been mediating between Khartoum and Juba on Abyei, said they must "ensure that the current situation does not spiral out of control."
Abyei's status has not been resolved despite steps which Sudan and South Sudan have taken since March to normalise their relations in other areas, after months of intermittent clashes along their undemarcated frontier.
Abyei's status was the most sensitive issue left unsettled when South Sudan split from Sudan in 2011. A referendum to determine Abyei's future was stalled and Sudanese troops shortly after took over the region by force.
Negotiations on the region's future are ongoing, but Benjamin said he believed the killings were "done by Misseriya militia... to frustrate the Abyei referendum."
However, Khartoum has insisted it remains committed "to all the agreements that have been signed" with Juba, adding that they hope the killings will not impact a recent warming of relations between the former civil war foes.
Around 4,000 Ethiopian troops with the UN Interim Security Force for Abyei (UNISFA) are based in the district.
South Sudan "has requested UNISFA search for the perpetrators to bring them to justice," Benjamin added, calling Saturday's attack "provocative killings".
"Sudan's government should also take steps to find out who committed this crime," he added.
Majok's death is the most serious incident since Sudanese troops withdrew in May last year to end a year-long occupation that forced more than 100,000 people to flee Abyei towards South Sudan.
While Sudan and South Sudan have been implementing timetables set out in March for restoring relations, they have not met deadlines they also agreed upon to set up Abyei's administrative structure, including a police service.