South Sudan's President Salva Kiir told U.S. Secretary of State John Kerry on Wednesday he intends to sign a peace deal to end a 20-month-old conflict, a State Department spokesman said.

"President Kiir assured the secretary that he has every intention of signing the peace agreement," spokesman John Kirby told reporters after Kerry called Kiir. "He said he needed a couple of more days of consultations but he made it very clear it was his intention to sign, which is encouraging."

Kiir told Kerry that he had some concerns that had now been addressed, Kirby added.

On Monday, Kiir refused to sign the deal brokered by regional leaders to end the conflict, which broke out in December 2013 when a political row between Kiir and his deputy Riek Machar spiraled into clashes.

Washington said on Tuesday it was consulting with other countries about imposing United Nations sanctions against South Sudan leaders who undermined the peace process.

"It is the actions of signing that matters (rather) than the pledge to do so," Kirby added.