Presidential Peace Advisor Ghazi Salah Eddin Atabani on Sunday urged the mediators to come back with "entirely new proposals" when talks resume in 10 days.
A sixth round of talks ended on Saturday with the two sides failing to agree on a draft peace accord in Nakuru, Kenya.
The trouble caused by the proposals "constitutes a setback in the ongoing negotiations," Atabani was quoted as telling Akhbar Al-Youm daily.
The proposals concern power- and wealth-sharing as well as security arrangements during an envisaged six-year period of autonomy for the south before a referendum to determine whether or not it remains part of Sudan.
The proposals were drawn up by mediators of the Kenya-based Intergovernmental Authority on Development IGAD, which groups seven east African states, including Sudan and Kenya.
Unity vs secession
Atabani put the blame mainly on the IGAD Secretariat whose proposals "differ largely" from the Machakos Protocol, a peace blueprint forged in Kenya last year, and from previous agreements.
They "pave the way for secession of southern Sudan while Machakos calls for unity," Atabani was quoted as saying.
He said the proposals place southern Sudan "entirely in the hands of the (rebel) movement and ignore other southern political groups and armed factions," which he believes would lead to instability after a peace deal.
Sudan's deputy ambassador to Kenya, Ahmed Dirdeiry said major sticking points include the document's proposal to set up two central banks for the north and south of the country, and exempt Khartoum from Islamic sharia law.
Sudan's deputy ambassador to Kenya, Ahmed Dirdeiry
Islamic law applies in all government-controlled regions.