Two warring factions from South Sudan are holding more advanced peace talks for the first time since conflict began in the country on December 15.
The talks are focusing on a ceasefire and the release of political prisoners.
Gunfire was heard in South Sudan's capital, Juba, on Saturday night.
South Sudan information minister Michael Makuei Lueth said forces loyal to Mr Machar instigated the violence, but that it was soon brought under control.
US Secretary of State John Kerry said the beginning of direct talks was an important step, but that both sides need to put the interests of South Sudan above their own.