* Tribal differences remain over who is eligible to vote
* Vote on secession due in January 2011
(Adds last key law passed paragraphs 16-17)
By Khaled Abdelaziz
KHARTOUM, Dec 30 (Reuters) - Sudan's parliament passed a law on Wednesday governing the oil-producing Abyei region's right to join the country's southern region if it secedes, or to remain part of the north.
But lawmakers said problems remained about who in Abyei would be allowed to vote on the question in a ballot that will coincide with a referendum in the south in a little over a year on whether southern Sudan should go its own way.
In a 2005 peace deal which ended more than two decades of civil war, Abyei was a major bone of contention and the region remains a possible flashpoint for a return to conflict.
The dominant northern National Congress Party and the former southern rebel Sudan People's Liberation Movement (SPLM), which formed a coalition government after the 2005 deal, voted for the law. But some lawmakers said significant problems remained.
The law allows for the people of Abyei, in central Sudan, to choose whether to remain in the north or join the south, which many analysts expect to secede in a simultaneous vote in January 2011.
It gives the Ngok Dinka tribe and other Sudanese who reside in Abyei the right to vote. A simple majority will decide the region's future.
Prominent lawmakers from the nomadic Missiriya tribe, who graze cattle a few months a year in Abyei, walked out of parliament, saying they wanted the same status as the Ngok Dinka.
"What happened today was a conspiracy against the Missiriya," said Mahdi Babo Nimr, a senior Missiriya figure.
The tribe has previously threatened military action if its demands are not met.
Parliament's deputy speaker said some details on who was eligible to vote had yet to be finalised.
"The referendum commission will decide on the criteria for residency in the region," said the SPLM's Atem Garang. "It is a deferred problem."
Garang said choosing the eight members of the referendum commission would in itself be a point of contention.
"It will be difficult to get people who are sincerely neutral," he said.
Abyei, whose people are among the poorest in Sudan, lies along the north-south border which is still not demarcated. Its potential as a flashpoint is increased by the fact that many of Sudan's oil fields traverse the contested north-south boundary.
Sudan's civil war claimed an estimated 2 million lives, drove 4 million from their homes and destabilised much of east Africa.
Parliament also passed a law on "popular consultations" for the states of Blue Nile and Southern Kordofan.
This gives residents there the right to voice a desire for more autonomy from Khartoum if they are unhappy with the government.
Many worry a separate south will have serious security problems as tribal violence has sharply escalated this year killing at least 2,000 people.
A witness said five Kenyans were shot, three killed, by a man wearing a south Sudan army uniform in the region's capital Juba on Monday night.
"The dead, one lady and two men, are still in the mortuary in Juba waiting to be transferred to Nairobi today," said Kenyan Lucy Wanjiku who saw the attack.
The independent web site Sudan Tribune quoted south Sudan army spokesman Kuol Diem Kuol as saying the army was investigating the attack.
Kuol also said that in separate violence on Monday, five south Sudan soldiers were killed in clashes with civilians.
(Additional reporting by Opheera McDoom and Marvis Byezza in Juba; editing by Robin Pomeroy)
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