South Africa's Deputy President Kgalema Motlanthe will challenge incumbent President Jacob Zuma for the leadership of the ruling African National Congress, his spokesman confirmed Thursday.

"He has informed the electoral commission that he will be accepting for all three positions he was nominated for. That is the president, the deputy-president and an additional member (of the national executive committee)," Motlanthe's spokesman Thabo Masebe told AFP.

On Wednesday a source close to Motlanthe told AFP the Deputy President would run.

The official confirmation ends months of speculation over Motlanthe's candidacy for the party's top job to be decided at its conference starting Sunday.

Around 4,500 senior ANC members will gather in Bloemfontein to select the party leader, who -- thanks to the party's electoral dominance -- is also likely to run Africa's largest economy until 2019.

Motlanthe, a former trade union leader, briefly served as interim president of the country in 2008-2009.