JUBA, South Sudan –  Officials in South Sudan say a tension-filled showdown in the middle of a market town between rebels and South Sudan's military led to the deaths of four civilians.

The United Nations on Monday said some 2,000 people are seeking refuge at a U.N. base fearing that more violence could follow.

The fighting took place Sunday in Pibor, where government forces have been trying to stamp out a rebellion by a former army colonel.

Beko Konyi, a spokesman for the Pibor County commissioner, said a confrontation broke out when one of the colonel's former commanders tried to enter the market but was stopped by soldiers. A grenade went off, and then gunfire, killing at least four people.

A U.N. spokesman, Kouider Zerrouk, described the situation Monday as calm but tense.