The UN Security Council is to consider a draft resolution from Belgium to end the UN mission monitoring the disputed border between Ethiopia and Eritrea.
The mandate for the UN's 1,700-strong peacekeeping force ends on Thursday.
Observers fear that if it stops, there could be a resumption of the fierce border war that ended in 2000.
Meanwhile, in discussions to extend the UN mandate in Darfur, some members are pushing for war crimes charges against Sudan's leader not to be pursued.
South Africa's ambassador to the UN, Dumisani Kumalo, says an increasing number of countries want the International Criminal Court to Djibouti troops killed on border ...
Three killed in Addis Ababa blast ... delay its moves to indict Sudan's President Omar al-Bashir.
South Africa and Libya, backed by Russia and China, want the UN Security Council to suspend the case against Mr Bashir but this is being resisted by other countries, led by the US and the UK.
On Monday, a group of mainly African relief and advocacy groups said the joint AU-UN force in Darfur - Unamid - was failing to protect civilians because it was too small and inadequately funded.
Only about a third of the intended 26,000 peacekeepers have been deployed.
"We are saying give peace a chance. Can you just give it a year, let's see Unamid deploying," Mr Kumalo said.
The UN estimates that five years of conflict in Darfur have left 300,000 people dead and more than 2 million people homeless.
Bitter border
In April, UN Secretary General Ban Ki-moon warned of a possible return to war if the peacekeepers pull out of Eritrea and Ethiopia.
BBC Africa analyst Martin Plaut says the war between the two neighbours that erupted in 1998 was the largest conventional conflict to have been fought on the African continent since the end of the Second World War.
Tanks, heavy artillery and modern aircraft were thrown into the fray and tens of thousands of people died in two-and-a-half years of bitter trench warfare.
The forces of the two nations are now are separated by a few hundred metres and the UN force has helped maintain a fragile peace, he says.
But the UN has already withdrawn most of its peacekeepers after Eritrea cut off fuel and food to the UN mission last year.
It was angered by Ethiopia's refusal to comply with a binding ruling from international arbitrators on where the border should run.
Ethiopian troops are stationed deep within the territory given to Eritrea, and Eritrea had demanded that the UN compel Ethiopia to withdraw.
However, there was no appetite at the UN for such direct intervention.
(BBC)
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