South Sudan has suspended pre-partition talks with the north, accusing Khartoum of planning to topple the south's government and kill its people.
Pagan Amum, a senior official with the south's ruling party, said Saturday that the north is training and arming militias to destabilize south Sudan and oust the region's leaders before secession in July.
Amum spoke again Sunday, saying the north's ruling party is arming Arab tribes so they can, in his words, carry out genocide like they have done in Darfur.
There was no immediate reaction from the north's ruling National Congress party to Amum's latest remarks. On Saturday, NCP officials dismissed Amum's accusations as baseless.
South Sudan has experienced a wave of deadly clashes with rebel groups in recent months. The south's army says at least 23 rebels were killed Saturday after they attacked Malakal, the capital of the south's oil-rich Upper Nile state.
Southerners overwhelmingly voted to declare independence from the north in a January referendum.
The vote was promised in a 2005 peace deal that ended Sudan's 21-year north-south civil war.
Fighting continues in Sudan's western Darfur region, where rebels took up arms against the government in 2003. The International Criminal Court has indicted President Omar al-Bashir on charges of war crimes and genocide in that region.
South Sudan is due to split away from the north on July 9. However, the sides have yet to settle several key issues, including the fate of the oil-producing Abyei region, which sits along the north-south border.