Khartoum — The joint political-security talks between Sudan and South Sudan that were scheduled to start on Wednesday in the Ethiopian capital have been postponed indefinitely, according to a news report.

The privately-owned Al-Shorooq TV said that the African Union mediation team led by Thabo Mbeki did not set a new date for the negotiations.

No reason was given for the delay but sources told the TV that the United States was behind the move over the slow pace of implementing the previous deals signed last September.

Sudan's President Omer Hassan Al-Bashir and South Sudan's Salva Kiir failed at talks in Ethiopia last month to end a stalemate over withdrawing armies from a border region - a pre-requisite for resuming oil exports.

Landlocked South Sudan shut oil output a year ago in a dispute over how much the new nation should pay in pipeline fees to Sudan to transport crude via its northern neighbor for export from Port Sudan on the Mediterranean.

Delegations from the two countries were to discuss modalities of the security arrangements. Khartoum accused Juba last month of making new demands on the demilitarized zone and of refusing to give up its alleged support to rebels from Sudan People Liberation Movement North (SPLM-N) in South Kordofan and Blue Nile.

The SPLM-N, made up of fighters who sided with the South during the civil war, controls part of the Sudan side of the border, which complicates setting up the buffer zone.

In a related issue the Sudanese army denied that any skirmishes erupted with South Sudan at the borders or that they have been any military buildup on their part.

"There is no truth to the accusation by South Sudan that we are amassing our troops along the border area and there are no armed battles between us and them, but there are existing tribal interactions that caused the recent armed conflict," Sudan army spokesperson Colonel al-Sawarmi Khalid Sa'ad said.

He also downplayed reports that South Sudan deployed troops to the borders saying that they have not monitored anything unusual.

Col. Sa'ad stressed that Juba has no capability or interest in going to war with Sudan.

Yesterday South Sudan's Kiir ordered the urgent and coordinated deployment of joint police and government troops to border areas with Sudan.

Juba accused Khartoum of building up troops and using militia groups to attack areas along the border in Unity state.