Ten people have been killed in an ambush of a convoy of south Sudanese civilians near the north-south border, a minister in the south has said.
Internal Affairs Minister Gier Chuang said 18 people were hurt in Monday’s attack in South Kordofan, north of the border, by Misseriya Arab tribesmen.
He said the civilians were returning home to vote in Southern Sudan’s ongoing independence referendum.
Some 30 people reportedly died earlier in the nearby disputed Abyei area.
On Tuesday, Southern Sudan is holding its third day of the week-long referendum, with voters looking set to back independence.
The vote was part of a 2005 peace deal which ended decades of civil war between the mainly Muslim north and the south, where most people are Christian or follow traditional religions.
“A convoy of returnees coming from the north to the south was ambushed… at about 1700 (1400 GMT) by armed Misseriya,” Mr Chuang told reporters in the southern capital Juba.
“Ten were killed and 18 were wounded. The attackers came in six or seven vehicles with guns,” the minister added.
Thousands of people living in the north have been returning home to the south to take part in the landmark referendum.
Misseriya tribesmen have made no public comment about the alleged attack.
The mostly nomadic cattle tribe was a key auxiliary militia of the North during the 1983-2005 conflict.
In a separate development, at least 30 people were killed in the oil-rich Abyei region on Monday, reports said.
One report said 20 policemen had been killed, but this was not confirmed.
Abyei was due to hold a separate referendum on whether to join north or south Sudan but this has been postponed indefinitely because of disagreements over eligibility.
Despite the violence, so far the referendum in Southern Sudan has been peaceful, the BBC’s Will Ross in Juba says.