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The longtime rivals, which split apart last year, have clashed repeatedly in their contested borderlands, while rows over oil payments have continued to stoke tensions.

The two edged dangerously close to resuming full-blown war in April when Juba seized the Heglig oil region, before withdrawing in the face of international pressure.

African Union-mediated talks to create a demilitarized zone resumed last week, but broke off on Thursday over conflicting versions of a boundary line, which both presented in lengthy press conferences, often coupled with jingoistic zeal.

Even as their delegates shook hands while slumped on the plush leather couches of a five-star Addis Ababa hotel, old wounds stemming from decades of conflict were on full display.

"Sudan is continuing its hostile propaganda against South Sudan and South Sudanese, including the president of Sudan," Pagan Amum, head of the South's negotiation team, said.

Sudan in turn accused its neighbor of stoking tensions by including five disputed areas on its map, including Heglig, which produced about half Sudan's oil output before the clashes.

Endorsement of South Sudan's version of the boundary line as a starting point for the demilitarized zone would mean Heglig would be incorporated inside the buffer zone and be subject to joint administrative status.

Sudan has insisted on using a boundary line used by the United Nations for operations purposes, while Juba displayed a map it said was introduced by Khartoum itself in the mid-1940s.

Sudanese Defense Minister Abdel Raheem Muhammad Hussein called South Sudan's move a "hostile action" on Thursday.

The two were expected to resume the talks "from the 21st onwards", South Sudan's Minister of Cabinet Affairs Deng Alor said.

The two sides also need to agree on how much the landlocked South should pay to export crude oil through Sudan.

Juba shut down its entire output of about 350,000 barrels per day in January to stop Khartoum seizing oil as compensation for what it called unpaid fees.

Further stepping up the rhetoric, negotiator Amum blasted Sudan's President Omar Hassan al-Bashir, wanted by the International Criminal Court, over a row about whether the leader would be able to attend an African Union summit scheduled for next month.

Bashir in 2009 became the world's first sitting head of state to be indicted for crimes against humanity and war crimes by the ICC - accusations he and other officials deny.

Malawi, which was set to host the African Union gathering of heads of state, moved to block Bashir from attending, prompting Sudan to ask the group to move the summit to Addis Ababa.

Amum described Bashir as a "criminal" and said he was a source of "embarrassment" for the continent's leaders.

Some 2 million people died in the civil conflict between north and south Sudan, waged for all but a few years between 1955 and 2005 over ideology, ethnicity, religion and oil.

(Editing by Michael Roddy)