Helen Zille campaigned for last month's election on an anti-Zuma platform
South African opposition leader Helen Zille has been labelled a racist by the governing ANC's Youth League for a lacerating attack on the president.
The Western Cape premier was quoted by the Sowetan newspaper as saying President Jacob Zuma had put his three wives at risk of contracting HIV.
She reportedly lashed out after union chiefs criticised her for appointing an all-male cabinet.
The ANC said it was "astounded" by the Democratic Alliance leader's remarks.
The war of words has erupted days after Mr Zuma reached out to opposition parties in a conciliatory speech at his inauguration.
The Sowetan on Tuesday quoted Ms Zille as saying: "Zuma is a self-confessed womaniser with deeply sexist views, who put all his wives at risk by having unprotected sex with an HIV-positive woman."
Self-proclaimed polygamist Mr Zuma was acquitted of rape in 2006 when he conceded having unprotected sex with his accuser, an HIV-positive family friend, but said he showered afterwards to prevent infection.
Ms Zille's remarks reportedly came in response to criticism from a Congress of South African Trade Unions' branch secretary, Tony Ehrenreich, that she is the only woman in the Western Cape executive council she unveiled on Friday.
Cosatu has said it will challenge the Western Cape premier's all-male cabinet in the Equality Court.
African National Congress spokesperson Jessie Duarte said in a statement: "Even by Zille's standards of personal invective, this latest attack is an unprecedented example of Zuma-hate. Zille's outburst is deeply offensive and should be roundly condemned."
Jacob Zuma promised "a new chapter" in ties with the opposition days ago
The ANC Youth League then waded in with a statement threatening to take militant action against Ms Zille if she continued to talk "hogwash".
The league said it was "disgusted by remarks attributed to the racist girl Helen Zille, who when failing to defend her stupid and sexist decision to appoint predominantly white males into her Cabinet, attacks the president".
Ms Zille's spokesperson, Fritz de Klerk, told the South African Press Association a response was being drafted.
The ANC won last month's general election, albeit with a slightly reduced majority, after a bitterly fought election campaign.
As he was sworn in on Saturday in Pretoria, Mr Zuma promised "a new chapter" in relations with the opposition, working together in the national interest.
"While appreciating a robust opposition, we also trust that we are able to move slightly away from the dogmatic approach that turns every issue into a contestation among parties," he said.