While Sudanese officials offered no comments on Saturday, SPLA sources said the talks, which opened on Monday, were "deadlocked and on the verge of collapse."
The sources said the talks had reached a stalemate after the Sudanese government refused to negotiate on the basis of a framework document drawn up by the Inter-Governmental Authority on Development, an east African regional body.
The SPLA wants the document to be the basis for ending Sudan's 20-year-old civil war.
Despite an agreement on granting the country's south the right to self-determination after a six-year transition period, the wrangle now is over power sharing and security arrangements.
"The whole world knows that there is a wonderful window of opportunity that has not to be missed"
Kenyan Foreign Minister Kalonzo Musyoka
The distribution of wealth during the interim period is another bone of contention.
But Kenyan Foreign Minister, Kalonzo Musyoka, expressed optimism that a deal could still be clinched despite the differences.
"The whole world knows that there is a wonderful window of opportunity that has not to be missed," Musyoka said.
"We hope to encourage the parties to continue negotiating in absolute good faith," he said.
Sudan's civil war between the north and the south has claimed at least 1.5 million lives and displaced four million people.
Meanwhile, a Sudanese newspaper quoted a government official as admitting that many civilians in North Dafur state have been executed by armed men acting in the name of the government.
The rebel Sudan Liberiation Movement had earlier accused pro-government militas of killing about 300 civilians.
The provincial governor, Yusuf Kibir, labelled the armed men as "outlaws" and refused to acknowledge any government responsibility for their acts.