UNITED NATIONS: The United Nations warned South Sudan's President Salva Kiir Tuesday that any political appointments must be consistent with a peace deal that ended nearly two years of civil war after Kiir replaced his vice president and rival Riek Machar.

Machar left the South Sudanese capital Juba earlier this month after an eruption of violence in the city when forces loyal to Kiir and Machar battled each other for several days with tanks, helicopters and other heavy weapons.

An August peace agreement states that the vice president must be chosen by the South Sudan Armed Opposition. However, Kiir replaced Machar on Monday with General Tabal Deng Gai, a former chief opposition negotiator who has broken ranks with Machar.

"Any political appointments need to be consistent with the provisions outlined in the peace agreement," U.N. spokesman Farhan Haq told reporters in New York Tuesday.

Kiir's appointment of Deng Gai – a former minister of mining – came after Kiir issued an ultimatum last week, demanding that Machar contact him within 48 hours and return to Juba to salvage the peace deal, or face replacement.

Deng Gai, who was the chief negotiator for Machar's SPLM-IO group during the peace talks, backed Kiir's ultimatum. Machar said on Friday he had fired Deng Gai and accused him of defecting to Kiir's party.

"We call on all parties to ensure that the ceasefire is maintained and that any divisions within the opposition or between the parties be dealt with peacefully through dialogue," Haq said.

South Sudan, which gained independence from Sudan in 2011, descended into civil war in 2013 after Kiir fired Machar as vice president. More than 10,000 people were killed and some 2 million displaced, many of whom fled to neighboring countries.