UN Security Council ambassadors met the leaders of South Sudan's warring sides on Tuesday in a bid to end eight months of conflict that has pushed the young nation to the brink of famine.
Brandishing the threat of sanctions, the diplomats arrived in the capital on a two-day visit to "engage with leaders" and witness "the humanitarian crisis first hand," British Ambassador Mark Lyall Grant said.
Thousands of people have been killed and over 1.5 million have fled almost eight months of carnage, sparked by a power struggle between President Salva Kiir and his sacked deputy Riek Machar, with battles between government troops, mutinous soldiers and ragtag militia forces divided by tribe.
The ambassadors are due to meet with Kiir before flying to the northern town of Malakal, one of the hardest hit areas in the fighting.
The town was left in ruins, swapping hands several times between government and rebels.
Foreign Minister Barnaba Marial told reporters that the diplomats would be "shown what South Sudan is doing with regard to peace."
The UN Security Council last week threatened to slap sanctions on leaders of both sides if fighting continues.
"The actions of President Salva Kiir and former vice president Riek Machar in continuing to pursue a military solution to this conflict are unacceptable," the 15-member council said on Friday.
The UN has said the food crisis is the "worst in the world", with aid workers warning of famine within weeks if conflict continues.
US Secretary of State John Kerry on Monday accused both sides of failing to commit to the peace process, a day after missing a key deadline to forge a unity government.
"Deadlines keep passing and innocent people keep dying," Kerry said.
Stop-start peace talks in the Ethiopian capital Addis Ababa which began in January officially restarted again last week, but the delegates have made little if any progress.
"This is an outrage and an insult to the people of South Sudan," Kerry said.
"Their leaders are letting them down again and again. Peace talks have been on-going in Ethiopia for six months, while the people of South Sudan continue to suffer and the war persists."
The United States and the European Union have already imposed penalties on three senior army commanders from the government and opposition, while the regional IGAD bloc have suggested they could follow suit if progress was not made.
Heavy fighting was reported Sunday around the eastern town of Nasir in Jonglei state, a former rebel headquarters wrested back by the government last month.
Both government and rebels blamed the other for the fighting.
Aid agencies have condemned what they say is a determination by leaders to try to defeat the other militarily.
"With the peace talks in Addis Ababa stalling, continuing violence throughout the country and a man-made food security crisis, the situation for South Sudan could not be more urgent," Oxfam's Tariq Riebl said in a statement.