UN leader Ban Ki-moon on Friday called on the UN Security Council to send more than 1,100 extra peacekeepers to the flashpoint region of Abyei disputed by rivals Sudan and South Sudan.
The call comes after deadly clashes in the territory between rival groups who Ban said "remain armed, hostile and highly distrustful of each other."
Rivalry has regularly turned into battles in Abyei, where sovereignty was never settled after South Sudan broke away from the north in July 2011.
Tensions hit a new peak with the May 4 killing of the paramount chief of the Ngok Dinka people, loyal to South Sudan, and an Ethiopian peacekeeper by gunmen from the Misseriya pastoralists considered supporters of the Khartoum government.
Ban said in a report to the UN Security Council that "the presence of armed groups" inside Abyei "remains a considerable security concern" and justified sending an extra 1,126 peacekeepers to the territory.
The UN Interim Security Force For Abyei (UNISFA) already has about 4,000 mainly Ethiopian peacekeepers in the territory. It is currently allowed to have have up to 4,200 troops.
Abyei is only about 10,500 square kilometers (4,000 square miles) and no other UN force has the same number of troops for the area.
But the annual migration of about 100,000 Misseriya with their 1.6 million cattle makes Abyei, normally dominated by the Ngok Dinka, a security tinderbox.
Ban highlighted the presence of the "Tora Bora militia group" inside Abyei as a further destabilizing influence.
Inter-communal murders that the Ngok Dinka and Misseriya blame on each other have also inflamed tensions.
While Sudan and South Sudan have strongly condemned the killing of the Ngok Dinka chief, neither side has yet met agreed deadlines for structures aimed at easing tensions.
They have failed to agree the makeup of an area council and government, nor even how to set up an Abyei police service.
Ban said the deadlock "continues to undermine efforts to stabilise the security and humanitarian situation" in Abyei. He said both governments had to act to prevent the entry of "unauthorized armed elements" into the territory.