"Every day brings fresh instances of a media that, in general terms, is politically and ideologically out of synch with the society in which it exists," ANC President Jacob Zuma wrote in a letter to ANC activists.

Zuma, who defeated South African President Thabo Mbeki for the ANC leadership last month, has had a testy relationship with the media. His supporters have accused public broadcaster SABC among others of having a pro-Mbeki tilt, especially in the coverage of the ANC leader's controversial corruption case.

The 65-year-old Zuma is due to go on trial in August for money-laundering, racketeering, fraud and corruption. Although he is the frontrunner to succeed Mbeki as state president in 2009, he has said he will stand down if convicted.

In his letter, Zuma said there was a trend in most mainstream media companies to adopt positions "antagonistic" to the ANC-led government and its efforts to transform South Africa since the end of white minority rule in 1994.

"At times, the media functions as if they are an opposition party," he said.

Zuma, whose close ties to trade unions and Communist politicians have raised investor fears, also criticised what he said was a scarcity of mainstream media outlets that adopted a "progressive left" political perspective.

He said the weekly letter from the ANC president, which was a staple when Mbeki led the party, would now only be published on special occasions.

The comments could stoke concerns among the media that a Zuma-led government may attempt to clamp down on press freedom, a charge that has been laid at Mbeki's government, which has denied that it is trying to muzzle dissent.

A proposed bill that allows pre-publication censorship in some cases has increased those fears. The government has said it is aimed only at those involved in child pornography.

Media groups and other critics have said the bill could be extended to other areas.

Others see the government's hand at work in a proposed takeover of Avusa, one of the country's most influential media groups and publisher of the Sunday Times, which has riled the ANC with its exposes of alleged corruption and wrongdoing.

Several Mbeki associates, including a political adviser, are involved in Koni Media Holdings' reported 7 billion rand takeover bid for Avusa, which was formerly known as Johnnic Communications Ltd.