UNITED NATIONS, Oct. 11 (Xinhua) -- The UN Security Council on Thursday decided to extend the UN peacekeeping mission in disputed Abyei region for the last time unless Sudan and neighboring South Sudan make "measurable progress" on their border demarcation.

In a unanimous vote to adopt Resolution 2438, the council renewed the mandate of the mission, or UNISFA, in Abyei between Sudan and South Sudan until April 15, 2019, by when the two countries are required to show progress in marking their border for the mission to stay longer.

Also, the resolution decided to maintain UNISFA's authorized troop ceiling of 4,500 until Nov. 15, 2018, and further decided that as of April 15 2019, the ceiling shall decrease to 3,959 troops, if the mission is to be extended.

According to the text, Sudan and South Sudan are expected to take seven specific measures in the next six months about their border demarcation, which include ensuring freedom of movement for UNISFA patrols, beginning to implement a timeline for verifying the functioning of the 10 border crossings and free movement across the border, and holding at least two meetings of the Joint Border Commission and Joint Demarcation Committee.

The oil-rich Abyei area is claimed by both Sudan and South Sudan. The 2005 peace deal that led to South Sudan's independence from Sudan six years later required the two sides to solve the issue but they have so far failed to do so.