Comcast's first £12.50 a share offer, valuing Sky at £22bn, resulted in Sky's independent committee recommending shareholders reject Murdoch's original £10.75 deal tabled in December 2016.
The fight for ownership of Sky is playing out against the backdrop of Disney and Comcast's battle for a raft of Fox assets, including Fox's current 39% stake in Sky.
But Disney and Fox are determined to keep their deal together - Murdoch has favored Disney in negotiations over the sale of 21st Century Fox assets, including Fox's stake in Sky, to Disney.More news: Trump dodges London protests for tea with Queen Elizabeth
Sky gives Fox and Comcast a rare opportunity to diversify out of the United States and reach more consumers directly.
Sky shares traded at £14.90 as of 9:55 am in London.
Following the announcement, Sky's share price was down 1.3 per cent at 14.81, though above the improved offer.
Last month, the U.S. Department of Justice gave the go-ahead to Disney's acquisition of the Fox assets, asking Disney, which owns sports network ESPN, to divest all of Fox's 22 regional sports networks, known as RSNs, on antitrust grounds. According to some shareholders, that has set an implied higher floor for Sky's shares. "Today's announcement further underscores Comcast's belief and its commitment to owning Sky", Comcast said in a statement.More news: Man dies as listeria outbreak recalls frozen food
The end of the week is also be the deadline for Comcast to post an offer to Sky shareholders, who then have 60 days to consider that offer under United Kingdom takeover rules.
Of course, there's still time for Comcast to make yet another counteroffer, forcing Disney to increase its bid once more.
The U.K. government, which has already said it's minded to approve Fox's bid for Sky after Fox satisfied concerns over media plurality, is due to deliver its final ruling on Thursday. News Corp., which is controlled by the Murdochs, withdrew its bid for Sky soon after.More news: Denver Broncos: Supplemental draft prospects of interest