Gerrie Nel, a senior official of South Africa's elite crime-fighting unit, called the Scorpions, was arrested at his home on Tuesday night. He has led the investigation of national police chief Jackie Selebi.

Moketedi Mpshe, acting head of the National Prosecuting Authority, told Talk Radio 702 that the arrest would not influence any action against Selebi. He said a decision on whether to prosecute him would be announced by the end of the month.

The Selebi investigation has the potential to damage South Africa's reputation at a time when it is trying to persuade sceptics that it can reduce high levels of violent crime ahead of the 2010 soccer World Cup, which it will host.

The embattled police chief has been accused of downplaying the severity of the country's crime problem and has raised eyebrows by acknowledging his friendship with Glenn Agliotti, a convicted drug smuggler.

South African media have reported that Selebi has ties to criminal syndicates. He has denied the allegations.

President Thabo Mbeki has stood by Selebi despite calls by the opposition and media for his dismissal, prompting allegations he was being protected for political reasons.

Selebi was an ANC activist in exile during the struggle to overthrow white minority rule.