South Sudan's President Salva Kiir has assured the US he will sign a peace deal to end the fledgling country's 20-month-old conflict, Washington said on Wednesday.

According to a US State Department spokesman, Kiir told Secretary of State John Kerry by phone on Wednesday he had every intention of signing the peace agreement.

"He said he need a couple of more days of consultations but he made it very clear it was his intention to sign, which is encouraging," said spokesman John Kirby.

On Monday, Kiir refused to sign the deal brokered by regional leaders, despite traveling to Addis Ababa over the weekend for the signing ceremony. One of his ministers had escribed the peace accord as a "sell-out."

South Sudan's civil war broke out in December 2013 when clashes erupted following a political row been Kiir and his deputy Riek Machar. The conflict took on an ethnic dimension and saw Kiir's Dinka people pitted against Machar's Nuer.

Following Kiir's decision, Washington warned it would call for a United Nations arms embargo against South Sudan and impose further targeted sanctions - unless the deal is signed.

A US diplomat said on condition of anonymity that a draft resolution would be circulated to the 15 Security Council members shortly.

Fighting resumed on Wednesday between government troops and rebel forces, a South Sudan military spokesman confirmed. Analysts said peace efforts were left in tatters as the warring sides blamed each other for attacks.

African Union Commission Chief Nkosazana Dlamini-Zuma warned that: "Deadlock in the peace process can only spell further disaster for South Sudan and its people, with far reaching implications for regional security and stability."

Around 200,000 people have been forced from their homes due to the fighting and nearly 70 percent of the population is facing food shortages.

mm/rc (AFP, AP, Reuters)