Sustained gunfire was heard in the South Sudanese capital Juba, as peace talks between rebels and the government faced further delays in neighbouring Ethiopia.
A reporter heard gunfire coming from the direction of the military headquarters of the government's Sudan People's Liberation Army forces.
South Sudan has been rocked by fighting that erupted last month in the capital, but quickly spread to other parts of the country.
Although Juba has been largely calm since the first days of the unrest, there was a brief gun fight last night and residents speak of growing tensions.
Rebel and government negotiators were supposed to begin their first face-to-face talks at 12.00pm in Addis Ababa with the aim of halting the clashes, which have killed more than 1,000 people.
But by 4.45pm Irish time, there was no sign of the two sides sitting down together.