Rupert Murdoch
Rupert Murdoch, the chairman of News Corp. and Twenty-First Century Fox Inc., pictured here in New York on Nov. 20, 2013. Reuters

Rupert Murdoch's Twenty-First Century Fox Inc. (NASDAQ:FOXA) offered $80 billion to buy Time Warner Inc. (NYSE:TWX) last month and was turned down by the media giant's board, multiple media outlets reported Wednesday.

The move by Murdoch comes as big media companies have been exploring mergers and acquisitions, in part to boost their leverage as large pay-TV operators combine. Comcast Corp. (NASDAQ:CMCSA) is in the process of acquiring Time Warner Cable Inc., and AT&T Inc. (NYSE:T) has bid for DirecTV (NASDAQ:DTV). In recent months, both Twenty-First Century Fox and Time Warner have been separating their entertainment and publishing businesses.

The New York Times reported that Fox offered $85 per share in stock and cash for Time Warner. At the time, that represented a 25 percent premium to Time Warner's stock price.

Under the takeover bid, which CNBC also reported, Fox had planned to sell Time Warner's CNN cable network, in a move aimed at appeasing antitrust regulators. Fox News Channel directly competes with CNN. Chase Carey, Fox's president and CEO, met with Time Warner CEO Jeff Bewkes in early June in a failed effort to sell the deal.

But after lengthy discussions, Time Warner's board earlier this month sent a "terse" response, saying the company could perform better standing alone, the reports said. Despite the snub, sources told CNBC that Murdoch remains "determined" to buy Time Warner.

The Times reported that Fox estimated that the proposed deal could generate cost savings of at least $1 billion, mostly by cutting staff.

Murdoch's interest in Time Warner emerged as one of the storylines last week at the annual Allen & Co. media conference in Sun Valley, Idaho. Besides Fox, rumors also arose that Google Inc. (NASDAQ:GOOGL) might also be interested in some type of deal. But when Variety magazine asked Bewkes about it at the conference last Wednesday, he replied: "I know nothing about it."