Uganda has deployed troops to South Sudan, the world's newest nation, as fears of civil war grow.
The United Nations said Monday that up to 180,000 people have been displaced due to the fighting in December.
The deposed vice president is Riek Machar, who has called for a negotiated cease-fire that includes a way to monitor compliance.
Kiir, the president, is from the south's biggest ethnic group, the Dinka, while Machar is an ethnic Nuer, the second-largest group in South Sudan.
Col. Philip Aguer, the South Sudanese military spokesman, said there was no major fighting over the weekend but tension remains.
Because "Machar has not committed himself to a cease-fire. We've not seen one." Pro-Machar forces still control Bentiu, the capital of oil-producing Unity state, and renegade troops are poised to attack Bor, the contested capital of Jonglei state, according to Aguer.