JUBA, Sudan (Reuters) - Sudan's ruling party said on Thursday that the southern army had killed nine of its officials during the first open elections in 24 years.

"Three days ago at night some (southern army) soldiers came to the home of the president of the National Congress Party in Raja, and killed him and eight other people -- they are also members of the NCP," Agnes Lokudu, head of the northern-dominated NCP in south Sudan, said.

Raja is in Western Bahr al-Ghazal state in south Sudan.

Lokudu said the killings were politically motivated by anger that many people in the area had voted for the NCP.

The ex-rebel Sudan People's Liberation Movement (SPLM), which dominates the southern government, denied the involvement of the separate south Sudan army.

"This was a passionate crime to do with a wife -- a feud that led to a shooting between the husband and lover," Suzanne Jambo, head of the SPLM's external relations office, said.

"This is not political."

Sudan's elections, entering the last of a five-day voting period on Thursday, had been largely free from major violence. A wave of opposition boycotts in much of the north left little competition for incumbent President Omar Hassan al-Bashir.

South Sudan's president and SPLM head Salva Kiir is also likely to be elected president of the semi-autonomous south.

But tensions have been high in the south between parties and independents opposing the SPLM who have complained of arrests and harassment.

Sudanese are voting in presidential, legislative and gubernatorial elections.