Rebel delegation chief Taban Deng told AFP he was committed to talks, but demanded the release of several top political leaders from the ruling Sudan People's Liberation Movement (SPLM), accused of involvement in the violence.
The Constitution was ratified by Sudan's National Assembly and the legislative council of the Sudan People's Liberation Movement (SPLM) on 8 July.
But these slights are as nothing, says the SPLM, to the failure of Mr Bashir's ruling National Congress Party (NCP) to implement the north-south peace agreement.
Like many in the South, he was confused by the decision of the SPLM to withdraw this week Yasir Arman, its presidential rival to Mr Bashir, and suspects a secret deal has been done: "All of a sudden in the middle of the river someone absconds," he says incredulously. "The reason given is not convincing to me".
The Nuer, the second-largest ethnic group, were represented by Machar, who became vice president of the Government of Southern Sudan and SPLM co-chair of the Joint Executive Political Committee.
Remains of dead cows and piles of dung are the only evidence of cattle in the area, after it was raided in an attempt to strip local Nuer communities, thought to be supporters of the Machar-led SPLM-IO, of their livelihoods.
After five years of SPLM rule, too many health and social indicators are slipping backwards.
The Sudan People's Liberation Movement (SPLM) grew out of the guerrilla army that fought a 20-year civil war with the Sudan government.
The main opposition party, the Sudan People's Liberation Movement (SPLM), made up of one-time southern rebels, withdrew its candidate, Yasir Arman, from the presidential contest, but it is unclear whether it is officially running for any other offices.
He said the fighting began when unidentified uniformed personnel opened fire at a meeting of SPLM, followed by an attack on army headquarters near the university carried out "by a group of soldiers allied to the former vice-president Dr Riek Machar and his group".
