South Sudan in July gained independence following a national referendum that came as the result of a comprehensive peace agreement signed in 2005.
Abdullahi Alazreg, the Sudanese envoy to the United Kingdom and Ireland, told the BBC that South Sudan lacks the administrative capacity needed for an independent state.
"South Sudan is not a real country," he said.
Since July independence, ethnic conflicts, disputes over oil and clashes over the ill-defined border separating the two countries has threatened to unravel the peace deal.
Alazreg said many of the outstanding issues left over from the 2005 peace agreement, which ended one of the bloodiest civil wars in modern history, weren't Khartoum's fault.
"We would like peace," he said.
Border talks between negotiators from Sudan and South Sudan broke down in early June.
Amnesty International last week estimated that from June 2011-April 2012, more than 114,000 people from Sudan fled to South Sudan while another 30,000 left for Ethiopia. Civilians along the border between Sudan and newly independent South Sudan are facing the worst of the crisis, the rights group said.