Kiir's term in office and that of the legislature expires at midnight according to terms of the transitional constitution adopted in 2011, Riek Machar said.
If Kiir refuses to resign, citizens have the right to overthrow his government, Machar said.
Machar also asked the international community withdraw its support for Kiir's government.
Machar's remarks come ahead of Thursday's independence day celebration, and throw the international backed mediation process between the two leaders into further disarray.
