The Sudan People's Liberation Movement protested the election of Ahmed Haroun, declared the winner of the governorship in petroleum-rich South Kordofan state, the BBC reported Monday.
"We will not accept these results because the vote was rigged," said Yasir Arman, head of the SPLM in the north.
South Sudan will become an independent state in July and analysts fear the dispute will spark another conflict in Sudan. Haroun is accused of complicity in the civil war in Darfur.
The ICC alleges that Haroun mobilized Arab militias to commit genocide against black African residents of Darfur in 2003-2004. Haroun said he is innocent.
Haroun defeated Abdelaziz al-Hilu, a senior official of South Sudan's SPLM, in the election.