LONDON (Reuters) - U.S. cable operator Comcast CMCSA.O has informally notified the European Commission of its intention to bid for Britain's pay-TV group Sky SKYB.L, triggering the regulatory process for the $31 billion deal.

FILE PHOTO: The NBC logo and Comcast are displayed on 30 Rockefeller Plaza, formerly known as the GE building, in midtown Manhattan in New York July 23, 2015. REUTERS/Brendan McDermid/File Photo

The world's biggest entertainment company shocked the market on Tuesday when it said it had approached Sky about a deal, challenging Rupert Murdoch's Twenty First Century Fox FOXA.O and Walt Disney Co DIS.N which had already hatched a complex plan to take control of the pay-TV group.

The Commission website shows no formal request has been made yet but a spokesman for Comcast said it had made an informal notification to get the ball rolling.

Comcast, the owner of NBC, CNBC and MSNBC, said it went public with its approach because it wanted to start the regulatory review. It believes it only has a narrow window to get the deal done before Fox nears completion of its own takeover of the 61 percent of Sky it does not already own.

Comcast’s action complicates a separate move by Disney to buy a range of Fox assets for $52 billion, including Sky, which was based on the assumption that Fox would complete its purchase.

Disney’s Bob Iger was in Paris when the news broke. He was quoted in Le Figaro newspaper as saying he had not yet studied Comcast’s provisional offer in detail.

“It does not compromise our agreement with Fox,” he said in the newspaper report. “In this agreement, Fox would bring over the 39 percent of the capital of Sky that it already holds, and would, furthermore, make an offer for the rest of Sky’s capital.”

Fox has said it remains committed to its cash offer announced in December 2016.

But investors are now hoping that Fox will make a higher offer or question whether Disney could make its own direct bid for Sky. Shares in Sky were trading at 13.40 pounds on Wednesday, above the 12.50 pounds offered by Comcast.

Fox agreed its deal to buy Sky in December 2016 but it has been forced to go through a comprehensive regulatory review after politicians raised concerns that Murdoch held too much influence in Britain. It agreed to buy Sky at 10.75 pounds per share.