In a briefing on March 30, Obi said rocket-propelled grenades, rockets and machine guns were pouring into Abyei. He said the heavy weapons could represent a new flashpoint in the tense relations between north and south.

"We have seen all sorts of armed elements that ordinarily are not supposed to be there," Obi said. "Both sides have these weapons, and we think they should abide by their own agreement and get them out of Abyei."

In March, at least 70 people were killed in two days of clashes in Abyei between rival tribes. The UN has called for the withdrawal of all forces from Abyei.

Khartoum has asserted that the south's Sudanese People's Liberation Army has deployed 2,500 troops in Abyei. The ruling National Congress Party said these troops have been wearing police uniforms.

SPLA said Khartoum was paying Arab tribes to infiltrate Abyei and other areas of southern Sudan. Abyei was not scheduled to secede along with the rest of southern Sudan and a referendum on the disputed region has not been set.

"There have been deaths, there have been displacements," Obi said. "And if the stalemate continues politically, the risk of confrontation remains and could escalate."

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