The U.S. envoy to South Sudan is urging the country's leaders to resume peace talks the day after lawmakers voted to extend President Salva Kiir's term by three years.

Donald Booth told reporters in South Sudan's capital, Juba, on Wednesday that the way to peace "is through negotiations" between the warring factions.

He said the best way to extend the government's constitutional legitimacy beyond July 9 — when Kiir's term was set to expire before the extension — "is through a peace agreement that would establish a transitional government of national unity."

South Sudan has been at war since December 2013 as government forces try to put down a rebellion led by Kiir's former deputy, Riek Machar.

Several peace agreements have failed to resolve the conflict.