South African rugby fans' anger has mounted over an off-key reggae singer who "butchered" their national anthem before the Springboks' Test match defeat by France at the weekend.

On Monday the South African Rugby Union wrote to their French counterpart expressing the nation's dismay at the performance before Friday night's match in Toulouse by an artist know as Ras Dumisani.

"As a union we were shocked and horrified by the rendition of the anthem, and I contacted the French Federation on Saturday morning to express our very grave concerns," said the union's president Oregan Hoskins.

French team manager Jo Maso said the choice of singer at each game was made by the visiting team's diplomatic staff.

"Every time we welcome a foreign side, we ask the embassy to propose people for the national anthems," said Maso.

"It's the South African embassy that put forward this man and we respected their choice."

Dumisani told local station Talk Radio 702 that he blamed the equipment for the poor sound, insisting that he had "sung beautifully", but that did little to douse the public outrage at his off-key performance of the four-language anthem.

The Young Communist League of South Africa described Dumisani's rendition of the anthem as "horrendous".

"Ras Dumisani is a chancer, a con-artist, a howler of note and a disgrace to our country and must be banned from singing the national anthem on official functions," said the league in a statement.

The league urged the government to compile a list of capable artists to avoid future embarrassments, especially ahead of next year's football World Cup.

Rugby fans have already filled websites with their anger, and a Facebook group "Ban Ras Dumisani from ever singing again" won 600 members just hours after opening.

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