South African President Jacob Zuma will miss a controversy-tinged EU-Africa summit in Brussels this week because of "other commitments", the country's foreign ministry said on Monday.

Pretoria would not say if Zuma's decision was taken in solidarity with long-time Zimbabwean President Robert Mugabe, whose government called for a boycott of the meeting after his wife, Grace, was refused a visa to attend.

The couple have been banned from visiting the European Union because of their role in rights abuses, but as Head of State Mugabe is still allowed to attend international forums.

Clayson Monyela, spokesman for South Africa's Department of International Relations and Cooperation, said on Monday that "the President has other commitments".

Zuma has battles to fight at home, where he has come under withering criticism for using $23 million (17 million euros) of taxpayers' money to upgrade his private family residence.

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A damning report last week found that he unlawfully benefitted from the improvements.

Elections are due to take place on May 7 and although Zuma's ANC is forecast to win, the vote is expected to be the most competitive since South Africa became a democracy in 1994.

At the two-day EU-Africa summit, which starts on Wednesday, South Africa will instead be represented by Minister of International Relations and Cooperation Maite Nkoana-Mashabane.

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South Africa's Foreign Ministry said the summit will "afford Africa and Europe the opportunity to further strengthen political and socio-economic cooperation between the two continents".

Mugabe, who is now aged 90 and has ruled Zimbabwe since independence in 1980, will chair the African Union next year, a one-year rotating post.