An Associated Press reporter saw heavily armed soldiers patrolling the streets of Juba Monday amid the gunfire emerging from Juba's main army barracks.
The streets were largely empty of civilians, with most Juba residents staying indoors.
EgyptAir reported that it had cancelled its flight to Juba on Monday, saying the airport there was closed.
The United Nations Mission in South Sudan on Monday reported the sound of mortar and heavy machinegun fire, saying hundreds of civilians had sought refuge inside U.N. facilities.
Tension had been mounting in the world's youngest nation since Kiir fired Machar as his deputy in July.
Machar, who has expressed a willingness to contest the presidency in 2015, said after he was fired that if the country is to be united it cannot tolerate a “one man's rule or it cannot tolerate dictatorship.”
His ouster, part of a wider dismissal of the entire Cabinet by Kiir, had followed reports of a power struggle within the ruling party.
