South Sudan's government and rebels were set to begin formal peace talks Sunday following a night of more fighting that sent more civilians fleeing the capital Juba.
The talks in the Ethiopian capital Addis Ababa are aimed at ending three weeks of fighting that have already left thousands dead in the world's newest nation.
US Secretary of State John Kerry urged the two sides not to use the talks as a "gimmick" for buying time.
"Negotiations have to be serious, there cannot be a delay, [a] gimmick in order to continue the fighting and try to find advantage on the ground at the expense of the people of South Sudan," Kerry told reporters while on a visit to Jerusalem Sunday.
After a preliminary meeting late Saturday, negotiations were expected to begin in earnest at 2 pm, diplomats said, with regional peace brokers struggling to prevent an early breakdown.
The spokesman for South Sudan's government delegation, Information Minister Michael Makuei, struck a confrontational tone by again accusing rebel leader Riek Machar of having started the fighting by attempting a coup.
"His attempt to overthrow a democratically elected government is an established fact, and not that only, but the way the international community is handling it is rather strange," he told reporters, rejecting calls for the government to release suspected rebels who are now in custody.
"They say these people have not committed anything, but why are people dying if there is no offence committed? Nobody is above the law, and whatever you do, if you are found in conflict with the law, whatever you are, you must be subjected to the law. This is our position."
"We are being told to negotiate with the rebels. But any rebels who have fallen in our hands will have to answer why he or she decided to take up arms against a democratically elected government," he added.
Machar has denied attempting a coup, and in turn accuses the president of conducting a violent purge of his rivals.