"The ... invitation ... will go a long way in building confidence in the peace process," a spokesman for Machar said in an emailed statement on Wednesday.
The spokesman further said Ethiopian Prime Minister Abiy Ahmed had invited Machar, who is under house arrest in South Africa, to attend the talks on June 20, Presstv reported.
According to the statement, the negotiations will be led by the eight-nation East African bloc of Intergovernmental Authority on Development (IGAD).
There was no immediate comment from Juba's government or from IGAD on the matter.
The bloody civil war in South Sudan, the youngest country in Africa, began in December 2013, when the incumbent president accused his former deputy, Machar, of plotting a coup. The two sides have been involved in a cycle of retaliatory killings that have split the impoverished country along the ethnic lines. Tens of thousands have been killed and millions displaced in the conflict.
The United Nations and other bodies accuse all sides in the war of committing atrocities against civilians.
In December 2017, South Sudan’s government and rebel groups inked a ceasefire agreement after talks in the Ethiopian capital, Addis Ababa. The deal, however, has been violated repeatedly with both sides blaming each other.
The meeting would be the first time that Kiir and Machar have met since August 2016.