Much of Abyei town has been destroyed in the clashes
Clashes in Sudan's oil-rich town of Abyei could pitch the north and south of the country into civil war again, a senior official from South Sudan says.
"We are on the brink of war," Pagan Amum, secretary general of the former rebel Sudan People's Liberation Movement (SPLM), told the BBC.
Up to 90,000 people have fled after a week of fighting and the disputed town is now controlled by northern soldiers.
A deal in 2005 ended years of war with the SPLM joining a unity government.
The BBC's Amber Henshaw in Sudan says oil-rich Abyei is at the heart of a bitter dispute between the north and south.
Both sides want it as their own, but its status remains contested more than three years after the Comprehensive Peace Agreement was signed, she says.
Our correspondent says there has been a lull in the violence in Abyei after a week of fighting which has left much of the town in ruins.
But Mr Amum said that there was a risk of the crisis escalating.
"We are not actually having options here; war... is not a good option. It is a possibility," he told the BBC's Focus on Africa programme.
"There are clashes that have already happened and forces are building up," he said.
With northern troops building up around the town, he said that southern troops were sure to follow.
The first steps to resolve the situation were to get the military out of the town and to deploy UN forces into the area, he said.
A northern official told the BBC he would not respond to Mr Amum's comments ahead of a high-level meeting between both sides expected to take place on Tuesday.
The 20-year north-south civil war, separate from the Darfur conflict, was said to have cost 1.5 million lives.
As part of the deal, nationwide elections are due to take place next year, to be followed in 2011 by a referendum on whether the south should secede.