* Abyei bone of contention between Sudan, South Sudan
* Tribal leader and Ethiopian peacekeeper killed in clash
KHARTOUM, May 5 (Reuters) - One Ethiopian peacekeeper was killed and two others wounded when a U.N. convoy was caught up in a tribal clash in the Abyei border region claimed by both Sudan and South Sudan, the United Nations said on Sunday.
Sudan and South Sudan in March agreed to resume cross-border oil flows and defuse tensions which have plagued them since the South seceded in 2011 after an independence vote.
But they were unable to decide on the ownership of Abyei, which both the Dinka tribe allied to South Sudan and the Arab Misseriya tribe allied to Sudan call their home.
Kuwal Deng Mayok, the top Dinka leader in Abyei, was travelling with a U.N. convoy when he was killed by members of the Misseriya in a clash on Saturday that risked fuelling new tensions in the flashpoint area.
An Ethiopian peacekeeper was also killed and two others seriously wounded by a Misseriya tribesman, U.N. Secretary-General Ban Ki-moon's office said.
"The Secretary-General urges the governments of Sudan and South Sudan and the ... Dinka and Misseriya communities to remain calm and avoid any escalation of this unfortunate event," it said in a statement.
Abyei straddles the border between the neighbours, who fought one of Africa's longest civil wars. It is prized for its fertile land and small oil reserves.
Like South Sudan, Abyei was meant to have an independence vote, agreed under a 2005 peace deal which ended the civil war between the north and south. But both countries have been unable to agree which tribe members should participate.
Ethiopian peacekeepers have been running a temporary administration for Abyei since Sudan seized it in May 2011 following an attack on a convoy of U.N. peacekeepers and Sudanese soldiers which the United Nations blamed on southern forces. Khartoum later withdrew its forces under a U.N. peace plan. (Reporting by Ulf Laessing in Khartoum and Lou Charbonneau in New York; Editing by Pravin Char)
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