A government-funded upgrade to South African President Jacob Zuma's private home worth nearly $29 million was a "scandalous" waste of taxpayers' money, the main opposition party said Monday.

The Democratic Alliance said it will lobby for more transparency about Zuma's rural village compound, which reportedly includes underground bunkers, a helipad and a clinic.

"The misuse of public money in revamping President Zuma's private homestead in Nkandla is growing evidence of a government that puts the enrichment of politically connected individuals above the interests of South Africans," DA parliamentary leader Lindiwe Mazibuko told reporters.

"While the economy is in crisis, and millions of South Africans find themselves unemployed and trapped in poverty, President Zuma's government is building a palace for him, as if he will be president for life."

The government so far has kept silent on the cost of "Nkandlagate", as the revamp has been dubbed, saying the private home had been declared a key point of national security.

Zuma insisted Monday that he had paid for all but the security costs involved in the upgrade.

"There has been an exaggeration of things," he said, adding that a public probe would make clear what had occurred. "I'm sure facts will make people understand what has happened."

Media reports have said the costs for Nkandla had soared to nearly 250 million rand (22.3 million euros) and that Zuma will only pick up five percent of the bill.

"The extravagant Nkandla upgrade is therefore not only a scandalous waste of public money, but it also bolsters the perception that President Zuma considers himself to be above the law," said Mazibuko.

The uproar over the lavish upgrade comes as South Africa has reined in spending in the face of slowing growth and rising debt, while millions of people still live in shantytowns and 16 million-plus receive state welfare grants.

The DA accused officials of flouting ethics legislation and spending rules on private home security and of using legal loopholes to hide the project's details.

It said it will introduce proposed amendments to tackle this, lobby for a probe by a parliamentary oversight committee and call again for a parliamentary debate on the "blatant abuse of power and public funds".

The project is already being investigated by the state's ombudsman.