(Reuters) - South Sudan has called off elections due in June and its cabinet plans to ask parliament to extend President Salva Kiir's term, a government spokesman said, as a violent power struggle between Kiir and former vice president Riek Machar rumbles on.

Thousands of people have been killed and more than a million have fled their homes since fighting between supporters of the two erupted in the world's newest nation in December 2013.

In a roadmap to peace agreed earlier this month, Kiir and Machar agreed the outlines of a power-sharing deal, and they are hoping to reach a final accord by the end of March.

Government spokesman Michael Makuei said that the proposal to extend Kiir and parliament's terms will be presented to lawmakers on Tuesday and that he was confident it will be approved.

"The cabinet decided yesterday to give peace a chance by calling off the elections and amending the constitution," Makuei told Reuters.

"The cabinet decided to extend the period of the life of the office of the president and Parliament."

Kiir's and parliament's terms were due to end in July. Makuei said the proposal to extend them was aimed at avoiding any power vacuum in the event that the government fails to reach a permanent deal with rebels it is fighting.

The two sides need a transitional government in place by July.

The cabinet has said new elections will now be held in 2017.

(Editing by George Obulutsa)