FIGHTING NEAR BOR

Lul Ruai Koang, military spokesman for the opposition, told journalists in Addis that rebel forces had attacked government troops near the town of Bor, near the capital.

Koang said his troops were near Juba and would await a command from the rebels' political leaders to attack the town if the peace talks break down. "We are ready, and once we are told what to do we'll get into action," he said.

In Juba, the government's military spokesman Philip Aguer said there had been fighting around Bor and elsewhere, including the Upper Nile state where some oil fields are located.

Politician David Yau Yau, who has in the past led a rebellion against South Sudan's army in the vast Jonglei state has joined the government troops, Aguer said. Yau Yau was not immediately available to comment.

The lack of progress in the peace talks has unnerved foreign powers who worry about a descent into full-blown civil war.

China called on Monday for an immediate ceasefire. The unrest has forced the government to cut oil production by about a fifth.

All of landlocked South Sudan's oil is piped through its northern neighbor, providing vital hard currency in transit fees for Khartoum. Oil major BP estimates that South Sudan holds sub-Saharan Africa's third-largest reserves.