The UK's biggest pay TV broadcaster Sky says it is withdrawing its recommendation to shareholders to accept 21st Century Fox's bid in a move that came just moments after Comcast placed a better offer on the table.

The US media giant Comcast, which owns NBC Universal and is the largest cable operator in the US - made a £22 billion ($30 billion) bid for Sky on Wednesday, topping a rival bid by Rupert Murdoch's Fox. Fox already owns a 39 percent stake in Sky and the media mogul had hoped to take complete control of the broadcaster that has 23 million retail customers in the UK.

Comcast CEO Brian Roberts says his company's cash offer values each Sky share at £12.50, 16 percent higher than the 21st Century Fox offer of £10.75 or £19 billion.

21st Century Fox issued a statement saying it remains committed to its offer and is "currently considering its options."

21st Century Fox has offered to insulate Sky's news operations from the influence of Murdoch and his family, who already own several other media titles in the UK - including The Times and hte best-selling tabloid, The Sun - to win approval of its bid.