Comcast is planning a $60 billion all-cash bid to top Walt Disney on its deal to acquire most of Twenty-First Century Fox's assets if the U.S. government approves AT&T's acquisition of Time Warner, according to people familiar with the matter.

The bid would top Disney's offer of $52 billion.

Comcast also plans to acquire 100 percent of U.K. satellite broadcaster Sky as part of an improved all-cash bid. If Disney gets into a bidding war with Comcast, then Comcast's bid for all of Sky and Fox could get close to $100 billion, these people said.

However, if the government shoots down AT&T-Time Warner, Comcast does not plan to bid.

Comcast is asking investment banks to increase the bridge financing facility they have already arranged for the Sky offer by as much as $60 billion to finance the Fox bid, Reuters previously reported.

Comcast originally touted its strong stock as a reason for Fox to accept a deal from the largest U.S. cable provider instead of Disney.

But Comcast shares have fallen about 15 percent since Disney announced its bid for Fox, and now Comcast thinks it has a better chance with an all-cash bid, even if Fox Executive Chairman Rupert Murdoch prefers Disney shares.

Comcast CFO Michael Cavanaugh said on the company's last earnings call, "Regarding potential acquisitions, it is our job to continuously evaluate whether there are opportunities for us to create value. But should we pursue anything while our stock is at these levels, while circumstances can always change, I think it is unlikely that we would use Comcast shares as a medium of exchange for a transaction."

Comcast believes Disney cannot match an all-cash bid for Fox because if it adds more stock to a deal, Fox stock will go down, depressing the value of the offer, sources told CNBC.

Reuters previously reported that Comcast was talking to banks about obtaining bridge financing in preparation for a possible all-cash bid.

Comcast declined to comment. Fox and Disney did not immediately respond to requests for comment.

—CNBC's David Faber and Reuters contributed to this report.

Disclosure: Comcast is the owner of NBCUniversal, parent company of CNBC and CNBC.com.

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