Broadcaster RTL is weighing up a buy-out offer from its major shareholder, the German media giant Bertelsmann.

RTL, the Luxembourg-based owner of the UK's Channel 5 television, said on Tuesday that its board is "considering" Bertelsmann's offer.

Bertelsmann's bid, worth a total of 650m euros ($578m), is set at 44 euros a share, below RTL's current share price of 45.3 euros.

The acquisition of RTL would mark the first stage in Bertelsmann's bid to take on global media giants AOL Time Warner and Vivendi Universal.

Expansion plans

Privately-owned Bertelsmann already has an 89% stake in RTL, having bought a 22% share in the broadcaster from Financial Times publisher Pearson last month.

Bertelsmann chief executive Thomas Middelhof is believed to be keen to build up the company, currently the world's fourth largest media business, ahead of a possible stock market flotation.

Analysts say the company is currently lagging behind AOL Time Warner of the US and Europe's Vivendi Universal, which have both managed to boost their transatlantic holdings through acquisitions.

Battle chest

Bertelsmann's profits are thought to have suffered during the media sector downturn, with music subsidiary BMG particularly hard hit.

But unlike its rivals, Bertelsmann has little debt, and is sitting on an estimated $6.75bn cashpile generated through the sale of its stake in AOL Europe.

The German media giant has previously attempted a partial takeover of UK broadcaster Carlton and a merger with music group EMI.

Its US subsidiaries include publishers Random House.