"The inauguration follows the ruling by the Constitutional Court of Zimbabwe on August 20 2013 that … Mugabe is the duly elected president of Zimbabwe," the international relations department said on Wednesday.
Motlanthe would be accompanied by International Relations Minister Maite Nkoana-Mashabane.
"President Jacob Zuma was among the first heads of state … to congratulate President Mugabe on 3 August 2013 following the announcement of the results by the Zimbabwean Electoral Commission," it said.
"In his statement, President Jacob Zuma reiterated South Africa's readiness to continue to partner with Zimbabwe in pursuit of mutually beneficial co-operation." A spokesperson for Zimbabwean opposition leader Morgan Tsvangirai told Agence France-Presse (AFP) on Wednesday that the Movement for Democratic Change leader would not attend the inauguration.
"Expecting Tsvangirai to attend the inauguration is like expecting a victim of robbery to attend a party hosted by the robber," Luke Tamborinyoka was quoted as saying.
AFP reported that Thursday had been declared a public holiday to allow people to attend Mugabe's swearing-in, to be held in a 60 000-seat sports stadium on the outskirts of Harare.
The ceremony was delayed after Tsvangirai challenged the election results in a petition to the country's constitutional court.
On Tuesday, the court cleared the way for the inauguration after ruling that the elections last month were "free, fair and credible".
Tsvangirai condemned the election as "a farce" and "a massive fraud" and demanded a forensic audit of the election results. – Sapa