South Africa's top corruption fighter has said President Jacob Zuma has "benefited unduly" from using state money to improve his rural residence.
The changes to Mr Zuma's private home, including a pool and cattle enclosure, cost taxpayers about $23m (£13.8m).
In a more than 400-page report, Public Protector Thuli Madonsela accused Mr Zuma of unethical conduct.
She said that Mr Zuma, who faces re-election in May, should repay costs for some of the unnecessary renovations.
The refurbishment of the residence in Nkandla, in Mr Zuma's home province of KwaZulu-Natal, has turned into a major political controversy in South Africa.
A government probe in December cleared President Zuma, who came to office in May 2009, of any wrongdoing, saying the improvements were needed for security reasons.
Correspondents say it was one of the reasons why Mr Zuma was booed in December at the memorial service for Nelson Mandela, South Africa's first black president.
'Bona fide mistake'
At a press conference in the capital, Pretoria, Ms Madonsela, South Africa's ombudsman, said the cost of the Nkandla upgrades were now estimated at 246m rand ($23m; £13.8m).
The original estimate for the work in 2009 was about 27m rand and the public protector launched her investigation in 2012 after it was reported that about 206m rand had been spent.
Her report, entitled Secure in Comfort, shows that the total amounts to eight times the money spent securing two private homes for Mr Mandela and more than 1,000 times that spent on FW de Klerk, South Africa's last apartheid-era president.
"The president tacitly accepted the implementation of all measures at his residence and has unduly benefited from the enormous capital investment in the non-security installations at his private residence," Ms Madonsela said, reading from the report's executive summary.
Correspondents say Mr Zuma has in the past repeatedly told parliament he used his own family funds to build his homestead.
The report said that while it could be "legitimately construed" that Mr Zuma had misled parliament over the renovations, it said it was a "bona fide mistake".
"Some of these measures can be legitimately classified as unlawful and the acts involved constitute improper conduct and maladministration," the public protector's said.
Ms Madonsela said Mr Zuma had 14 days to respond to her report before parliament.
The BBC's Andrew Harding says the report comes just two months before the governing African National Congress (ANC) faces national elections.
Mr Zuma has successfully brushed aside previous scandals, but Nkandla seems to have touched a particular nerve, he says.
The ANC is not about to lose power, but its popularity is shrinking, our correspondent adds.