The UK's largest online property portal has rejected a third bid from Rea Group, the digital property company owned by Rupert Murdoch's News Corp.

The board of Rightmove unanimously voted to turn down the revised cash-and-shares offer just two days after receiving it, saying it was "unattractive" and undervalues the business at £6.1 billion. It further noted that the implied value of 770p per share had fallen to 759p as of Wednesday due to a decline in Rea's share price.

Rea, which is majority-owned by News Corp, called on Rightmove shareholders to urge the company's directors to engage in "constructive discussions" to work towards a recommended transaction. It added that it remains ready to "engage immediately" with the board of Rightmove.

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"Rea is disappointed by the latest rejection from the board of directors of Rightmove and is frustrated that, save for the rejection of Rea's three previously disclosed proposals, Rea has still had no substantive engagement with Rightmove," the company said.

Since its initial £5.6bn bid on September 5, Rea has increased its offers with the latest one about £200m higher than the £5.9bn put forward on 20 September. Under City Takeover Panel rules it now has until September 30 to make a revised or walk away.

Rightmove made a pre-tax profit of £259.8m last year on revenues that rose by 10% to £364.3m. It advertises more than one million properties each month and raises cash by charging estate agents subscription fees to list properties, as well as selling other services.

Rupert Murdoch's son Lachlan bought Rea in 2001 and the property company has taken on increasing importance following the sale of some of News Corp's major media assets and the retirement of the elder Mr Murdoch last year.

Rea is now worth some £13.3bn and News Corp’s overall digital real-estate services division, which includes operations in the US, accounted for a third of total global profits in the year to the end of June. The UK's housing market is approximately triple the size of Australia's, meaning a deal would substantially expedite Rea's international growth plans.

In a note to investors earlier this week after Rea unveiled its latest offer, AJ Bell investment director Russ Mould noted that "you must pay a premium price" if you want to own the market leader, and "that's exactly the situation with Rightmove".

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“Rupert Murdoch’s Rea Group is back for the third time with a higher bid for the UK property portal, but it still doesn’t look like the price is generous enough," Mr Mould said. "Shareholders are more likely to sit up and show interest if the bid starts with an eight, not a seven – and so the latest bid of 770p is a step in the right direction but unlikely to be enough.

“This looks like a serious pursuit, albeit one where the bidder’s idea of fair value still doesn’t align with shareholders’ expectations.”

He added: “There is only so much of a song and dance you can do with takeovers. Rea really needs to show its best and final offer. If it’s still not enough to win over Rightmove’s board and shareholders, the bidder needs to walk away and think about different ways to expand its empire.”

Shares in Rightmove closed yesterday's trading 10.6p lower at 672.4p.