UNITED NATIONS — The Security Council voted unanimously Thursday to extend the U.N. peacekeeping force in the disputed Abyei region on the Sudan-South Sudan border for the last time unless both countries demonstrate “measurable progress” on marking their border.

A resolution adopted by the U.N.’s most powerful body sets out seven specific measures that Sudan and South Sudan must take in the next six months for the force to remain, at a reduced level of just under 4,000 troops.

Both Sudan and South Sudan claim ownership of the oil-rich Abyei area. The 2005 peace deal that led to South Sudan’s independence from its northern neighbor in 2011 required both sides to work out the final status of the oil-rich Abyei region, but it is still unresolved.

The measures the council spelled out that Sudan and South Sudan must take include complete withdrawal by both countries from the Safe Demilitarized Border Zone, and a start to implementing a timeline for verifying the functioning of 10 border crossings and free movement across the border.

They must also ensure freedom of movement for U.N. peacekeeping patrols and hold at least two meetings of the Joint Border Commission and Joint Demarcation Committee before March 15, 2019, and resume negotiations on disputed areas.

The resolution extends the mandate of the U.N. peacekeeping mission, known as UNISFA, until April 15, 2019, with the current troop ceiling of 4,500 until Nov. 15, 2018.

The council said that if it determines that Sudan and South Sudan have demonstrated “measurable progress on border demarcation” and decides to extend the mandate after April 15, 2019, the troop ceiling will be reduced by 541 troops to 3,959 troops.

UNISFA has been in Abyei since 2011 and both Sudan and South Sudan welcomed the council’s unanimous decision to extend its mandate.

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