The conflict in Sudan's western region of Darfur could endanger the peace deal in the south, a senior southern rebel commander says.
Many thousands are starving in Darfur, aid workers say
Abdel Aziz Adim said the SPLA would not co-operate with a planned coalition government if it "crushes" Darfur.
The SPLA and the government are putting the final touches to a deal to end 21 years of war in the south.
About one million people have fled Darfur, where Arab militias are accused of targeting black Africans.
Both conflicts pit black African groups against the Arab-dominated government but they have been largely separate.
"We will not be party to a government that will crush the people of Darfur," Mr Adim said.
"They have a just cause and I personally will not be ready to work with such a government."
Some human rights campaigners say the pro-government Janjaweed militia are conducting a genocide against Darfur's black African population.
US war crimes envoy Pierre Prosper has said there is evidence of a possible genocide, but UN Secretary General Kofi Annan refuses to use that description.
At least 10,000 people have been killed and aid workers say that may more will die from hunger in refugee camps, where food has run short.
United States Secretary of State Colin Powell is due to visit Sudan on Tuesday and Wednesday and is expected to travel to Darfur.
On Sunday, talks between the SPLA and the government resumed in Kenya.
After two years of talks, they have agreed to set up a power-sharing government, with autonomy for the south for six years.
A referendum is then due to be held on whether the mainly Christian and animist south should secede from the Muslim-dominated north.
Both sides of the conflict in Darfur are Muslim, but rebels accuse the government of ignoring the region.