Beer giant Interbrew has said that media reports claiming it was poised to bid for South African Breweries were based on falsified documents.

The Belgian-based brewer has said that, while some parts of the leaked takeover briefing were authentic, others "appear to be a complete fabrication, or to have been altered in a misleading way".

Analysis of a retrieved document has found that while the bulk of it is accurate, extra text, suggesting Interbrew would offer a 30% premium for SAB shares, had been added.

SAB shares soared 8% to 478p on Thursday following press reports of the takeover.

Interbrew has reported its findings to stock exchanges in London and Belgium, and was considering whether to call in further authorities including the police, a spokesman told BBC News Online.

"As our investigation goes along, we will decide whether to call in other authorities as appropriate," the spokesman said.

'Only a proposal'

Interbrew admitted that the document, drawn up by bankers, had considered the possibility of taking over South African Breweries, the world's fifth largest brewer.

But the company dismissed the briefing as a "preliminary working document" which was part of a routine review of rival brewers, and had not been presented to directors.

The briefing had originally suggested that the firm merged with SAB at nil-premium, with falsified text suggesting a premium should be paid.

Interbrew has apologised over the takeover rumours, which SAB chief executive Graham Mackay branded as "truly astonishing".

SAB shares closed up 8p at 480p in London on Friday.